[utils] Implement rewindable bitmap

[danlaine]

Work in progress

[Copilot]

Pull Request Overview

This PR implements a rewindable bitmap wrapper called Historical that maintains a current state plus diffs for tracking history and batching operations. The implementation provides diff-based snapshots, atomic batch operations with read-through semantics, and the ability to reconstruct any historical state.

Key changes:

• Adds a new Historical bitmap wrapper with batch-based mutation system
• Implements reverse diff tracking to reconstruct historical states
• Provides atomic batch operations with automatic abort on drop

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
utils/src/bitmap/mod.rs	Exports the new Historical, BatchGuard, and Error types
utils/src/bitmap/historical.rs	Complete implementation of the rewindable bitmap with extensive documentation and tests

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[Copilot]

[nitpick] Using core::mem::forget in tests can lead to resource leaks and makes the test harder to understand. Consider restructuring the test to avoid needing mem::forget, perhaps by extracting the panic-inducing code into a separate function.

Suggested change

	let mut historical: Historical<4> = Historical::new();
	let _batch1 = historical.start_batch();
	// This should panic because a batch is already active
	// We need to use core::mem::forget to prevent drop from clearing the batch
	core::mem::forget(_batch1);
	start_second_batch_panics();
	}
	fn start_second_batch_panics() {
	let mut historical: Historical<4> = Historical::new();
	let _batch1 = historical.start_batch();
	// This should panic because a batch is already active

[codecov]

Codecov Report

❌ Patch coverage is 95.37522% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.15%. Comparing base (9c7abdc) to head (a009707).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
utils/src/bitmap/historical.rs	95.71%	48 Missing ⚠️
utils/src/bitmap/prunable.rs	82.35%	3 Missing ⚠️
utils/src/bitmap/mod.rs	80.00%	2 Missing ⚠️

@@            Coverage Diff             @@
##             main    #1717      +/-   ##
==========================================
+ Coverage   92.10%   92.15%   +0.04%     
==========================================
  Files         307      308       +1     
  Lines       79648    80794    +1146     
==========================================
+ Hits        73362    74455    +1093     
- Misses       6286     6339      +53     

Files with missing lines	Coverage Δ
utils/src/bitmap/mod.rs	97.04% <80.00%> (-0.15%)	⬇️
utils/src/bitmap/prunable.rs	98.22% <82.35%> (-0.50%)	⬇️
utils/src/bitmap/historical.rs	95.71% <95.71%> (ø)

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