refactor(sink): remove sink vnode bitmap update handling

[wenym1]

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What's changed and what's your intention?

This PR removes the update-vnode-bitmap path from sink execution and sink coordination. Sink actors now reject unexpected update-vnode-bitmap barriers instead of trying to apply them in place.

The main changes are:

• Remove update-vnode-bitmap request handling from sink coordinator RPC/meta coordination code.
• Remove new_vnode_bitmap propagation through sink log-store barriers and related flush/seal callbacks.
• Simplify KV/in-memory log-store reader and writer logic by deleting bitmap-update serialization, buffering, and replay paths.
• Keep sink config update handling in execute_consume_log, including skipping no-op config updates without rewinding/restarting the log reader.

This relies on the assumption that sinks will not receive in-place vnode bitmap updates. If such a barrier reaches a sink actor, the actor returns an error while handling the barrier.

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

No user-facing release note. This is an internal sink/log-store coordination refactor.

Testing

• cargo fmt --all -- --check && cargo clippy --all-targets --all-features

[wenym1]

• refactor(sink): remove sink vnode bitmap update handling #26575 👈 (View in Graphite)
• main

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