chore: use U256 for EthBigInt

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• use U256 as an underlying type for EthBigInt - this is better because there's no heap allocation involved there (U256 vs sign + vec)

Reference issue to close (if applicable)

Closes #4436

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Refactor

  • Updated internal representation of RPC integer types for improved compatibility and consistency across financial value responses (base fees, gas prices, balances, and transaction fees).

• Bug Fixes

  • Refined gas price validation logic to ensure accurate detection of non-zero values in RPC responses.

[coderabbitai]

Walkthrough

EthBigInt is migrated from a num_bigint::BigInt-backed wrapper to an ethereum_types::U256-backed wrapper. Bidirectional From conversions between EthBigInt, BigInt, and TokenAmount are added. All construction sites across eth RPC handlers and trace submodules are updated to use the new From/into() API.

Changes

EthBigInt U256 migration

Layer / File(s)	Summary
EthBigInt type redefinition and From impls src/rpc/methods/eth.rs	Removes the BigInt-backed EthBigInt definition with custom serde/get-size logic, replaces it with a U256-backed wrapper, and adds From<BigInt>, From<&BigInt>, From<u64>, From<EthBigInt> for BigInt, and From<EthBigInt> for TokenAmount impls. Removes the big_int_heap_size_helper import and TODO comment.
RPC handler construction sites src/rpc/methods/eth.rs, src/rpc/methods/eth/types.rs, src/tool/subcommands/api_cmd/api_compare_tests.rs	Updates eth_baseFee, BaseFeeByHeight, eth_gasPrice, eth_getBalance, receipt gas fee/cap, reward-percentile premium, and eth_maxPriorityFeePerGas to use .into() or EthBigInt::from(...). Updates EthCallMessage → Message value conversion and changes the EthGasPrice API test to check non-zero instead of positive.
RPC handler serde test src/rpc/methods/eth.rs	Updates gas_price_result_serde_roundtrip to construct EthBigInt via U256::from(i) and assert equality after encode/decode.
Geth trace module migration src/rpc/methods/eth/trace/geth.rs	Updates build_account_snapshot_from_entries and all prestate/diff-mode balance assertions in tests to use EthBigInt::from(...). Removes unused num::BigInt test import.
State diff module migration src/rpc/methods/eth/trace/state_diff.rs	Updates build_account_diff and all balance diff assertions in unit and EVM actor scenario tests to use EthBigInt::from(...). Removes num::BigInt test import.
Trace types test migration src/rpc/methods/eth/trace/types.rs	Migrates all EthBigInt construction sites in AccountState, AccountDiff, StateDiff, and EthTrace→GethCallFrame tests/helpers to EthBigInt::from(...). Removes num_bigint::BigInt test import.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• ChainSafe/forest#6289: Directly touches EthBigInt in src/rpc/methods/eth.rs, adding GetSize impls that are now removed by this PR's migration to U256.
• ChainSafe/forest#6412: Modifies the same src/rpc/methods/eth.rs and src/rpc/methods/eth/trace/* files, adding Ethereum trace call result types that depend on the EthBigInt representation changed here.

Suggested labels

RPC

Suggested reviewers

• hanabi1224

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: refactoring EthBigInt to use U256 instead of BigInt.
Linked Issues check	✅ Passed	The PR successfully addresses issue #4436 by replacing rpc::eth::BigInt with ethereum_types::U256 as the underlying type.
Out of Scope Changes check	✅ Passed	All changes are scoped to updating EthBigInt implementations and related test updates; no unrelated modifications detected.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch eth-big-int-type

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch eth-big-int-type

Warning

Review ran into problems

🔥 Problems

Stopped waiting for pipeline failures after 30000ms. One of your pipelines takes longer than our 30000ms fetch window to run, so review may not consider pipeline-failure results for inline comments if any failures occurred after the fetch window. Increase the timeout if you want to wait longer or run a @coderabbit review after the pipeline has finished.

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.40%. Comparing base (ead4de9) to head (683f2bf).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/rpc/methods/eth.rs	88.88%	2 Missing and 1 partial ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/rpc/methods/eth/trace/geth.rs	81.18% <100.00%> (ø)
src/rpc/methods/eth/trace/state_diff.rs	80.74% <100.00%> (ø)
src/rpc/methods/eth/trace/types.rs	93.60% <100.00%> (-0.02%)	⬇️
src/rpc/methods/eth/types.rs	65.71% <100.00%> (ø)
src/rpc/methods/eth.rs	65.09% <88.88%> (+0.26%)	⬆️

... and 11 files with indirect coverage changes

---

Continue to review full report in Codecov by Harness.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cbdbc78...683f2bf. Read the comment docs.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.