consumer: improve performance of EventsGroup (#5941)

[ti-chi-bot]

This is an automated cherry-pick of #5941

What problem does this PR solve?

Issue Number: close #5937

What is changed and how it works?

• AppendMessage records whether the message is out of order or not, with the overhead of comparing neighboring CommitTs just once.
• In normal order, ResolveInto uses sort. Search to find message boundaries with CommitTs <= resolveTs directly, instead of traversing all the search, instead of traversing all messages at once and allocating temporary resolved slices.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

  Scenario, 16K messages	Before	After	Improvement
  No messages resolved	139.9 µs/op	14.6 ns/op	roughly 9,500×
  Half resolved	161.4 µs/op	7.16 µs/op	roughly 22.5×
  All resolved	175.6 µs/op	8.06 µs/op	roughly 21.8×

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Please refer to [Release Notes Language Style Guide](https://pingcap.github.io/tidb-dev-guide/contribute-to-tidb/release-notes-style-guide.html) to write a quality release note.

If you don't think this PR needs a release note then fill it with `None`.

Summary by CodeRabbit

• Performance

  • Improved event resolution when messages arrive out of timestamp order.
  • Optimized processing of buffered events, including partial and complete resolution scenarios.

• Tests

  • Added benchmark coverage for ordered, out-of-order, partial, and full event resolution across large message sets.

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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