Record label edits as delta patches

[nabeya11]

Changes

Label edits (label / relabel / unlabel) now mutate labels in place and record only the delta.

• Only the indices and previous values of points whose label actually changed are recorded.
• relabel / unlabel became nearly identical loops and are consolidated into mutateLabels.
• With in-place edits, the pre-edit PointCloud object is mutated after an edit. Existing tests that relied on it being untouched now create a fresh cloud per test case.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.86%. Comparing base (04661d1) to head (b964e52).

Files with missing lines	Patch %	Lines
patch.go	72.54%	8 Missing and 6 partials ⚠️
editor.go	93.10%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                  Coverage Diff                   @@
##           perf/patch-history     #360      +/-   ##
======================================================
- Coverage               45.93%   45.86%   -0.07%     
======================================================
  Files                       9        9              
  Lines                    1585     1598      +13     
======================================================
+ Hits                      728      733       +5     
- Misses                    808      813       +5     
- Partials                   49       52       +3     

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[Copilot]

Pull request overview

This PR changes label-edit operations (label/relabel/unlabel) to mutate the point cloud in place while recording undo history as compact “delta” patches containing only the indices and prior label values that actually changed.

Changes:

• Add a new labelPatch patch type with encode/decode support and revert logic.
• Update label-edit flows to apply in-place updates and consolidate relabel/unlabel loops via mutateLabels.
• Update/add tests to account for in-place mutation and validate label patch behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
patch.go	Introduces labelPatch, plus uint32-slice encoding/decoding utilities and decode support for the new patch type.
editor.go	Switches label-related edits to in-place mutation and records undo as labelPatch deltas; consolidates relabel/unlabel via mutateLabels.
patch_test.go	Adds a labelPatch revert test and includes label patches in encode/decode roundtrip coverage.
command_test.go	Refactors tests to use fresh point clouds per case due to in-place mutation semantics.

Suppressed comments (1)

editor.go:190

• mutateLabels pushes an empty labelPatch when no labels changed, creating a no-op undo step. Since this is now an in-place edit, the forced runtime.GC() is also likely unnecessary overhead.

	e.push(p)
	runtime.GC()
	return nil

---

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

patch.go:212

• writeUint32s allocates a temporary 4*len(vs) byte slice and then copies it into the bytes.Buffer. For large label patches this adds significant peak memory overhead (and extra copying) exactly when trying to keep undo deltas small. Writing each uint32 directly to the buffer avoids the extra allocation.

func writeUint32s(buf *bytes.Buffer, vs []uint32) {
	b := make([]byte, 4*len(vs))
	for i, v := range vs {
		binary.LittleEndian.PutUint32(b[i*4:], v)
	}
	buf.Write(b)
}