Save obliterate sequence number on zero-length obliterates

[titrindl]

This PR fixes how we save the obliterate sequence number on the associated pendingSegmentGroup. Previously, the sequence number would never be set for zero-length obliterates, so we would get stuck considering the obliterate as unsequenced.

This PR also surfaces zero-length obliterates in mergeTreeDeltaCallback as long as the obliterate's endpoints are not equal.

[msfluid-bot]

Code Coverage Summary

↑ packages.dds.sequence.src:
Line Coverage Change: 0.02%    Branch Coverage Change: 0.05%

Metric Name	Baseline coverage	PR coverage	Coverage Diff
Branch Coverage	89.48%	89.53%	↑ 0.05%
Line Coverage	89.85%	89.87%	↑ 0.02%

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Baseline commit: 5156eb4
Baseline build: 305838
Happy Coding!!

Code coverage comparison check passed!!

[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated no suggestions.

Comments skipped due to low confidence (3)

packages/dds/merge-tree/src/mergeTree.ts:1253

• Ensure there are tests that cover scenarios where obliterateInfo is undefined.

if (pendingSegmentGroup.obliterateInfo !== undefined) {

packages/dds/merge-tree/src/mergeTree.ts:2108

• Ensure there are tests that cover scenarios where the start and end positions or sides are equal.

if (start.pos !== end.pos || start.side !== end.side) {

packages/dds/merge-tree/src/mergeTreeNodes.ts:706

• The assignment to obliterateInfo.seq has been removed. If obliterateInfo.seq is used elsewhere, this could introduce a bug. Ensure obliterateInfo.seq is set correctly.

moveInfo.movedSeqs[seqIdx] = opArgs.sequencedMessage!.sequenceNumber;

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[titrindl]

@anthony-murphy I had to merge the sequence changes into this PR because there were two tests failing on assert 0x2d8.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +475 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	463.74 KB	463.87 KB	⯅ +132 Bytes
azureClient.js	562.69 KB	562.74 KB	⯅ +49 Bytes
connectionState.js	724 Bytes	724 Bytes	■ No change
containerRuntime.js	261.99 KB	262 KB	⯅ +14 Bytes
fluidFramework.js	426.65 KB	426.66 KB	⯅ +14 Bytes
loader.js	134.18 KB	134.19 KB	⯅ +14 Bytes
map.js	42.71 KB	42.71 KB	⯅ +7 Bytes
matrix.js	148.32 KB	148.36 KB	⯅ +43 Bytes
odspClient.js	528.43 KB	528.48 KB	⯅ +49 Bytes
odspDriver.js	97.84 KB	97.86 KB	⯅ +21 Bytes
odspPrefetchSnapshot.js	42.81 KB	42.83 KB	⯅ +14 Bytes
sharedString.js	164.17 KB	164.27 KB	⯅ +104 Bytes
sharedTree.js	417.11 KB	417.11 KB	⯅ +7 Bytes
Total Size	3.36 MB	3.36 MB	⯅ +475 Bytes

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Baseline commit: 3c27751

Generated by 🚫 dangerJS against 17313f0