fix(drive): replace silent epoch u16 truncation with checked conversion

[QuantumExplorer]

Issue Being Fixed or Feature Implemented

Security audit found that mtd.epoch as u16 silently truncates u32 values > 65535. A malicious node returning epoch = 65536 in metadata would cause the client to verify against epoch 0 instead, potentially accepting a proof for the wrong epoch.

What Was Done

• Replace all as u16 casts in proof verification with try_u32_to_u16() checked conversions that return an error on overflow
• Fix applies to epoch indices from both request fields and response metadata
• Also fixes unchecked limit and offset truncations in the same file
• Removed redundant manual MAX_EPOCH guard in favor of the existing try_u32_to_u16() helper

How Has This Been Tested?

• Unit tests verify try_u32_to_u16 errors on epoch > u16::MAX (65536, u32::MAX, 100000)
• Unit tests verify normal epochs still work (0, 1, 42, u16::MAX)
• Unit tests verify u32_to_u16_opt errors on overflow and works for valid values
• cargo test -p drive-proof-verifier passes (4 new tests)
• cargo clippy -p drive-proof-verifier clean
• cargo fmt --all clean

Breaking Changes

None. This only changes error behavior for values that were previously silently corrupted.

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 made corresponding changes to the documentation

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 34263861-3cac-467b-8bc9-6c279f1514de

📥 Commits

Reviewing files that changed from the base of the PR and between 658d02d and 419e320.

📒 Files selected for processing (1)

• packages/rs-drive-proof-verifier/src/proof.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/epoch-u16-truncation

📝 Coding Plan

• Generate coding plan for human review comments

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.28%. Comparing base (658d02d) to head (419e320).
⚠️ Report is 28 commits behind head on v3.1-dev.

Additional details and impacted files

@@             Coverage Diff              @@
##           v3.1-dev    #3293      +/-   ##
============================================
- Coverage     70.42%   68.28%   -2.15%     
============================================
  Files          3293     3293              
  Lines        262598   262598              
============================================
- Hits         184931   179310    -5621     
- Misses        77667    83288    +5621     

Components	Coverage Δ
dpp	56.61% <ø> (-1.82%)	⬇️
drive	74.76% <ø> (-3.44%)	⬇️
drive-abci	81.44% <ø> (-1.49%)	⬇️
sdk	30.34% <ø> (-0.91%)	⬇️
dapi-client	39.08% <ø> (ø)
platform-version	∅ <ø> (∅)
platform-value	39.35% <ø> (ø)
platform-wallet	60.40% <ø> (ø)
drive-proof-verifier	∅ <ø> (∅)

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[QuantumExplorer]

Approved