[Pipe] Support region-level realtime downgrading

[Caideyipi]

Description

Per-Pipe region-level downgrade ordering

• Add source.realtime.region-level-downgrading and its legacy extractor.* alias, disabled by default. Each Hybrid source reads the option from its own Pipe parameters.
• When enabled, serialize downgraded TsFiles at DataRegion level. A later TsFile cannot pass until the previous TsFile and all tablets generated from it have been committed.
• Leave downgrade only after all downgraded TsFiles complete, and stop forwarding realtime tablets through USING_BOTH while region-level downgrade is active. This preserves ordering for equal-timestamp data with serialize-by-region and realtime-first=false.

Bounded latest-TsFile tail

• Retain a bounded realtime tail only for the latest TsFile so flushes cannot continuously chase and prolong downgrade.
• Promote the previous tail to TsFile transfer when a newer epoch arrives, while preserving events queued before downgrade.

TsFile lifecycle

• Track generated-tablet completion for both processor conversion paths.
• Keep the TsFile progress index until the final generated tablet commits.
• Restrict raw-tablet commit hooks to progress-reporting or TsFile-derived events.

Verification

• DataNode test compilation.
• Node Commons and DataNode compilation with both English and Chinese locales.
• DataNode and Node Commons Spotless checks.
• PipeRealtimeExtractTest: 10 tests passed, including enabled/disabled Pipe isolation.
• git diff --check.

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This PR has:

• been self-reviewed.
  • concurrent read and write
• added comments explaining the intent of non-obvious logic.
• added or updated unit tests to cover the new code paths.

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Key changed/added classes (or packages if there are too many classes) in this PR

• PipeRealtimeDataRegionHybridSource
• PipeTsFileInsertionEvent
• PipeRawTabletInsertionEvent
• PipeEventCollector
• PipeSourceConstant
• PipeRealtimeExtractTest