refactor(test): cleanup /cannon test structure and documentation

[aliersh]

This PR refactors part of the test suite within the /cannon folder as part of a broader effort to standardize structure, documentation, and formatting across the codebase.

The goal of this PR is to land the straightforward refactors first. More complex files, due to custom setup logic, heavy internal dependencies, or unclear structure, will be handled in a follow-up PR to avoid blocking progress and reduce review scope.

Common changes applied where applicable:

• Consolidated shared test initialization into dedicated *_TestInit contracts
• Organized test functions into logically separated contracts inheriting from TestInit
• Added @title and @notice tags to all test contracts
• Added function-level @notice comments describing expected behavior under test
• Replaced @dev tags with @notice where appropriate
• Enforced a 100-character limit for inline comments

Progress

Refactored 2 of 3 test files (66.6% complete)

• MIPS64.t.sol
• MIPS64Memory.t.sol
• PreimageOracle.t.sol (deferred)

This remaining file will be refactored in a future PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.55%. Comparing base (03d70f8) to head (9f24091).
Report is 40 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #16211      +/-   ##
===========================================
- Coverage    82.49%   81.55%   -0.94%     
===========================================
  Files          161      161              
  Lines         8866     8866              
===========================================
- Hits          7314     7231      -83     
- Misses        1412     1502      +90     
+ Partials       140      133       -7     

Flag	Coverage Δ
cannon-go-tests-64	65.84% <ø> (-1.94%)	⬇️
contracts-bedrock-tests	96.24% <ø> (ø)

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see 8 files with indirect coverage changes

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