test(contracts): improve DisputeMonitorHelper test coverage

[devin-ai-integration]

test(contracts): improve DisputeMonitorHelper test coverage

Summary

Enhances the DisputeMonitorHelper test suite by converting focused tests to fuzz tests and adding edge case coverage:

• toRpcHexString: Added edge case test for zero value (0x0) and fuzz test verifying output prefix format
• search: Converted test_search_olderThanEverything_succeeds and test_search_newerThanEverything_succeeds to proper fuzz tests with bounded timestamp parameters
• getUnresolvedGames: Converted test_getUnresolvedGames_betweenTimestamps_succeeds to fuzz test with parameterized timestamps and gap

The original tests used vm.randomUint() internally but weren't parameterized fuzz tests. Converting them to proper fuzz tests with bound() constraints provides broader coverage across the input space.

Review & Testing Checklist for Human

• Verify the bound constraints in fuzz tests are appropriate (e.g., type(uint64).max - 1 for newer search to allow +1 without overflow)
• Run just test-dev --match-path test/periphery/monitoring/DisputeMonitorHelper.t.sol -v to confirm all 16 tests pass

Notes

• All tests passed locally (16 tests, 0 failures)
• No production code changes - test-only modifications
• Link to Devin run: https://app.devin.ai/sessions/9da777165afc48ceb1d43ff7f9c6a2df
• Requested by: Ariel Diaz (@aliersh)

[devin-ai-integration]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.60%. Comparing base (3549f71) to head (3f2f62c).
⚠️ Report is 2050 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #18732      +/-   ##
===========================================
+ Coverage    73.97%   77.60%   +3.63%     
===========================================
  Files          190      135      -55     
  Lines        11322     7291    -4031     
===========================================
- Hits          8375     5658    -2717     
+ Misses        2801     1633    -1168     
+ Partials       146        0     -146     

Flag	Coverage Δ
cannon-go-tests-64	?
contracts-bedrock-tests	77.60% <ø> (ø)

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see 55 files with indirect coverage changes

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