dynamicstream: remove batch configuration from the stream level, and support it at the area level

[3AceShowHand]

What problem does this PR solve?

Issue Number: close #xxx

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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

• New Features

  • Configurable event-collector batching for changefeeds: count and byte limits.

• Enhancements

  • Batch-size and batch-byte settings exposed across sinks and dispatcher so the event collector can apply batching.
  • Streaming components adopt a shared, configurable batching mechanism.

• Tests

  • Added unit and integration tests validating batching behavior, defaults, and overrides.

• Refactor

  • Generalized batching infrastructure and updated memory-control logic for adaptive pause/resume.

[gemini-code-assist]

Summary of Changes

Hello @3AceShowHand, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the batching configuration within the dynamicstream utility. It shifts the responsibility of defining batching parameters from the individual stream level to the AreaSettings level. This change introduces a more modular and policy-driven approach to batching, allowing for greater flexibility and potentially more granular control over how events are batched.

Highlights

• Configuration Refactoring: Removed BatchCount and BatchBytes fields from the Option struct, signifying the removal of stream-level batch configuration.
• New Batching Policies: Introduced new interfaces and structs (sizePolicy, countPolicy, bytesPolicy) to define flexible batching policies.
• Area-Level Batching: Relocated batching configuration by adding a batcher field to the AreaSettings struct, enabling batching to be configured at the area level.

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[gemini-code-assist]

Code Review

This pull request refactors batching configuration by removing it from the stream-level Option and introducing it at the area-level via AreaSettings. This is achieved by adding a batcher field to AreaSettings and defining new sizePolicy, countPolicy, and bytesPolicy types to handle different batching strategies. My review has identified a critical issue regarding the initialization of the new batcher field, which could lead to a nil pointer dereference. I've also pointed out a minor inconsistency in receiver naming for better code maintainability. Please address these points to ensure the stability and clarity of the new implementation.

[3AceShowHand]

/test all

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign flowbehappy for approval. For more information see the Code Review Process.
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[3AceShowHand]

/test all

[3AceShowHand]

/test all

[3AceShowHand]

/test all

[ti-chi-bot]

@3AceShowHand: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cdc-mysql-integration-light-next-gen	c60f623	link	false	/test pull-cdc-mysql-integration-light-next-gen
pull-unit-test	d9b544c	link	true	/test pull-unit-test
pull-unit-test-next-gen	d9b544c	link	false	/test pull-unit-test-next-gen
pull-check	ae12398	link	true	/test pull-check

Full PR test history. Your PR dashboard.

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[3AceShowHand]

/retest

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456.

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[3AceShowHand]

/test all