feat: size metrics for chain follower internal hash maps

[hanabi1224]

Summary of changes

Changes introduced in this pull request:

# HELP chain_follower_tasks_size_bytes Size of the chain follower tasks in bytes
# TYPE chain_follower_tasks_size_bytes gauge
# UNIT chain_follower_tasks_size_bytes bytes
chain_follower_tasks_size_bytes 544
# HELP chain_follower_tasks_len Length of the chain follower tasks
# TYPE chain_follower_tasks_len gauge
chain_follower_tasks_len 1
# HELP chain_follower_tasks_cap Capacity of the chain follower tasks
# TYPE chain_follower_tasks_cap gauge
chain_follower_tasks_cap 14
# HELP chain_follower_tipsets_size_bytes Size of the chain follower tipsets in bytes
# TYPE chain_follower_tipsets_size_bytes gauge
# UNIT chain_follower_tipsets_size_bytes bytes
chain_follower_tipsets_size_bytes 83984
# HELP chain_follower_tipsets_len Length of the chain follower tipsets
# TYPE chain_follower_tipsets_len gauge
chain_follower_tipsets_len 67
# HELP chain_follower_tipsets_cap Capacity of the chain follower tipsets
# TYPE chain_follower_tipsets_cap gauge
chain_follower_tipsets_cap 1772

Reference issue to close (if applicable)

Closes

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

Release Notes

• Monitoring & Observability
  • Introduced Prometheus metrics collectors for chain synchronization tasks and state-machine operations with detailed monitoring capabilities.
  • New gauges expose allocation size, data structure length, and capacity metrics for internal synchronization components.
  • Enhanced metrics coverage provides comprehensive visibility into synchronization task performance and internal resource utilization patterns.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 4f2defad-516c-4762-9daf-17052b8a92b9

📥 Commits

Reviewing files that changed from the base of the PR and between a79a337 and 1702561.

📒 Files selected for processing (1)

• src/chain_sync/chain_follower.rs

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Walkthrough

This PR adds Prometheus metrics instrumentation to the chain synchronization module. It updates imports, decorates the state machine with custom debug output, introduces wrapper types that implement the Collector trait to expose internal container metrics, and registers these collectors during ChainFollower initialization.

Changes

Synchronization metrics instrumentation

Layer / File(s)	Summary
Imports and state machine debug annotation src/chain_sync/chain_follower.rs	Import adjustments add chrono::Utc and hashbrown types; SyncStateMachine gains a derive_more::Debug derive that skips bad_block_cache from debug output.
Collector implementation for synchronization metrics src/chain_sync/chain_follower.rs	SyncTasks and SyncStateMachineWrapper wrapper types implement prometheus_client::Collector to expose gauges for allocation size, length, and capacity of internal HashSet and HashMap collections.
Metrics registration in ChainFollower src/chain_sync/chain_follower.rs	Prometheus collectors are registered during ChainFollower::new for the sync task set and wrapped state machine, exposing chain follower gauge metrics.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• akaladarshi
• LesnyRumcajs
• sudo-shashank

🚥 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
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: adding Prometheus metrics for sizes of internal HashMaps and HashSets in the ChainFollower component.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ 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 hm/metrics-for-chain-follower-hashmaps

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/metrics-for-chain-follower-hashmaps

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[codecov]

Codecov Report

❌ Patch coverage is 5.26316% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.34%. Comparing base (a79a337) to head (1702561).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/chain_sync/chain_follower.rs	5.26%	72 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/chain_sync/chain_follower.rs	33.37% <5.26%> (-2.90%)	⬇️

... and 4 files with indirect coverage changes

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