feat(stream): deprecate no-shuffle backfill creation

[wenym1]

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What's changed and what's your intention?

Deprecate creating new no-shuffle backfill jobs while preserving compatibility for existing persisted jobs.

• Frontend planning now selects SnapshotBackfill when available and otherwise falls back to ArrangementBackfill for MV, index, vector index, and sink creation.
• streaming_use_arrangement_backfill and the related developer config remain accepted for compatibility, but are marked deprecated and ignored for new streaming jobs.
• Legacy no-shuffle BackfillExecutor now drains the remaining snapshot immediately after the initial barrier at the committed previous epoch before consuming upstream messages again.
• Planner and runtime backfill tests were updated to cover MV, index, and sink fallback behavior.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.
• I have added fuzzing tests or opened an issue to track them.
• My PR contains breaking changes.
• My PR changes performance-critical code, so I will run (micro) benchmarks and present the results.
• I have checked the Release Timeline and Currently Supported Versions to determine which release branches I need to cherry-pick this PR into.

Documentation

• My PR needs documentation updates.

Release note

New streaming jobs no longer use no-shuffle backfill. If snapshot backfill is unavailable, RisingWave uses arrangement backfill instead. The streaming_use_arrangement_backfill session variable is deprecated and ignored for new streaming jobs, while existing no-shuffle backfill jobs remain compatible.

[wenym1]

• feat(stream): deprecate no-shuffle backfill creation #25963 👈 (View in Graphite)
• main

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