logpuller: control region scan admission with memory quota

[lidezhu]

What problem does this PR solve?

Issue Number: close #5519

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

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ca4f9ce0-be14-446c-89b9-8da95dae6162

📥 Commits

Reviewing files that changed from the base of the PR and between 825a0b3 and 4a8d179.

📒 Files selected for processing (21)

• logservice/logpuller/memory_quota.go
• logservice/logpuller/memory_quota_test.go
• logservice/logpuller/region_admission_controller.go
• logservice/logpuller/region_admission_controller_test.go
• logservice/logpuller/region_event_handler.go
• logservice/logpuller/region_event_handler_test.go
• logservice/logpuller/region_event_sink.go
• logservice/logpuller/region_event_sink_test.go
• logservice/logpuller/region_request_scheduler.go
• logservice/logpuller/region_request_scheduler_test.go
• logservice/logpuller/region_request_store.go
• logservice/logpuller/region_request_store_test.go
• logservice/logpuller/region_request_worker.go
• logservice/logpuller/region_request_worker_test.go
• logservice/logpuller/subscription_client.go
• logservice/logpuller/subscription_client_test.go
• metrics/grafana/ticdc_new_arch.json
• metrics/nextgengrafana/ticdc_new_arch_next_gen.json
• pkg/config/debug.go
• pkg/config/debug_test.go
• pkg/metrics/log_puller.go

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ldz/refactor-puller06

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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