Stop contending for the shared rayon pool when summing entry sizes

[CleanCut]

We don't need to send entries to individual threads in a thread pool in order to read their num_bytes field. 🤣

ENG-1250

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 5c166a28-31af-4e5f-9c1a-97628962ef64

📥 Commits

Reviewing files that changed from the base of the PR and between ebab2cc and 2c66092.

📒 Files selected for processing (1)

• crates/liboxen/src/repositories/entries.rs

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📝 Walkthrough

Summary by CodeRabbit

• Performance
  • Updated entry size calculation to use a streamlined sequential approach.
• Maintenance
  • Removed an internal parallel-processing dependency from this calculation.

Walkthrough

The entry size calculation in entries.rs now uses sequential iteration. The Rayon prelude import was removed. The calculated total remains the sum of all entry byte sizes.

Changes

Entry size calculation

Layer / File(s)	Summary
Sequential entry size summation crates/liboxen/src/repositories/entries.rs	Removed the Rayon import. Changed compute_entries_size from into_par_iter to iter while preserving the summed byte-size result.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: avoiding contention on the shared Rayon pool during entry-size summation.
Description check	✅ Passed	The description explains why serial summation is sufficient and identifies the related tracking issue.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cleancut/entries-size-serial-sum

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