feat: Add latest_commit field to LogSegment

[DrakeLin]

What changes are proposed in this pull request?

Add latest_commit field to LogSegment to prepare for in-commit timestamp (ICT) support. When ICT is enabled, we need access to the latest commit file to read timestamp information. We cannot depend on ascending commits because commits will be filtered out by checkpoint processing when checkpoint version equals commit version.

Changes

• Add latest_commit_file: ParsedLogPath field to LogSegment (mandatory)
• Add latest_commit_file: Option<ParsedLogPath> field to ListedLogFiles (optional)
• Track latest commit during listing, before any checkpoint filtering occurs
• Handle incremental snapshot updates by inheriting latest_commit from existing snapshot when new listing is empty

How was this change tested?

Added and changed tests to verify latest commit is passed through

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 84.80%. Comparing base (d3c7323) to head (ed8ff83).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
kernel/src/snapshot.rs	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1363      +/-   ##
==========================================
- Coverage   84.81%   84.80%   -0.01%     
==========================================
  Files         113      113              
  Lines       28647    28659      +12     
  Branches    28647    28659      +12     
==========================================
+ Hits        24297    24305       +8     
  Misses       3196     3196              
- Partials     1154     1158       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.