fix(drive): replace expect/unwrap with error propagation in production code

[QuantumExplorer]

Issue being fixed or feature implemented

Production code in fetch_compacted_nullifiers and verify_compacted_nullifier_changes used .expect() which would panic on invalid data instead of returning errors.

What was done?

Replaced .expect() calls with map_err + ? error propagation in functions that return Result. Retained .expect() only inside find_map closures where ? isn't available, with safety comments explaining the preceding length guard.

How Has This Been Tested?

• cargo check -p drive — compiles cleanly

Breaking Changes

None.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

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[github-actions]

✅ DashSDKFFI.xcframework built for this PR.

• Workflow run: https://github.com/dashpay/platform/actions/runs/22760152112
• Artifacts: DashSDKFFI.xcframework (folder), DashSDKFFI.xcframework.zip, xc_checksum.txt

SwiftPM (host the zip at a stable URL, then use):

.binaryTarget(
  name: "DashSDKFFI",
  url: "https://your.cdn.example/DashSDKFFI.xcframework.zip",
  checksum: "1875cda69634f772229711862dbec2f3e6e2f02843bc1dc1f113cd6add762ae2"
)

Xcode manual integration:

• Download 'DashSDKFFI.xcframework' artifact from the run link above.
• Drag it into your app target (Frameworks, Libraries & Embedded Content) and set Embed & Sign.
• If using the Swift wrapper package, point its binaryTarget to the xcframework location or add the package and place the xcframework at the expected path.