fix(meta): clean dropped table change logs and watermarks

[wenym1]

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What's changed and what's your intention?

Dropping a subscription can mark its table change log for complete garbage
collection. The meta-store deletion path previously represented this operation
with u64::MAX, then cast it to the signed meta-model Epoch type. The cast
produced -1, so the resulting checkpoint_epoch < -1 predicate matched no
rows and left the table's change log permanently orphaned.

This PR:

• Represents complete table change-log deletion explicitly and deletes all rows
  for the affected table, while preserving epoch-based truncation for active
  tables.

• Removes table watermarks for every table in removed_table_ids, including
  drops that carry no new watermark update.

• Adds a unit test covering watermark removal when applying a Hummock version
  delta.

• Closes Bug: hummock_table_change_log accumulates orphaned rows permanently after subscription drop, causing meta leader degradation #26011

Validation

• cargo fmt --check
• git diff --check main...HEAD
• CARGO_PROFILE_DEV_DEBUG=0 CARGO_BUILD_JOBS=1 cargo test -p risingwave_hummock_sdk --lib test_apply_version_delta_removes_dropped_table_watermark
• CARGO_PROFILE_DEV_DEBUG=0 CARGO_BUILD_JOBS=1 cargo clippy --all-targets --all-features

Checklist

• I have added necessary unit tests and integration tests.
• I have added test labels as necessary.

Documentation

No user documentation update is required. The operational impact is covered by
the release note below.

Release note

Dropping subscriptions and watermark-bearing materialized views now cleans up
their associated Hummock change-log and watermark metadata, preventing orphaned
metadata from accumulating in the meta database.

[wenym1]

• fix(meta): clean dropped table change logs and watermarks #26413 👈 (View in Graphite)
• main

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