feat(index): support partition-scoped global index drops

[QuakeWang]

Purpose

drop_global_index declared partitions but rejected it, while the core builder could only drop matching indexes across all partitions.

Brief change log

• Add core partition predicates and structured SQL partition parameters.
• Reject invalid parameters before deletion; preserve dry-run and snapshot-guarded commits.
• Reuse Java FLOAT formatting and preserve signed-zero and NaN partition matching.

Tests

80 focused tests passed, covering partition selection, retained index definitions, invalid parameters, floating-point regressions, dry-run, and stale snapshots. CI-pinned formatting, strict Clippy, dependency and license checks passed.

API and Format

Adds GlobalIndexDropBuilder::with_partition_filter. No storage format changes.

Documentation

Document structured partitions syntax in the procedure module.

[JingsongLi]

Requirement fit: SUPPORTED. Implementation: FINDINGS at 47b42b4. Partition-scoped index maintenance has end-to-end value, but the new SQL parser can drop a different LTZ partition's index from the one requested.

Validated against the integration merge with main ae858ea: all 49 original SQL procedure tests, 17 core drop tests, 39 partition-format tests, and the stale-snapshot commit guard pass. An independent actual SQL write/build/select/selective-drop probe also preserves query results. A second actual SQL probe under TZ=Asia/Shanghai, with nonlegacy LTZ partitions, reproduces the wrong-partition deletion described inline. Please cover this supported timezone/partition-format combination before production use.