feat(scan): support deletion vector cardinality

[luoyuxia]

Purpose

Linked issue: close #201

Support deletion vector cardinality in index manifest metadata so scan planning can preserve the value when building deletion files.

Brief change log

• introduce DeletionVectorMeta to replace the raw (offset, length) tuple used by deletion vector ranges
• deserialize and serialize optional _CARDINALITY from index manifest metadata
• propagate deletion vector cardinality into DeletionFile during table scan planning
• add a unit test for cardinality propagation and refresh the index manifest fixture test to use the production reader and current fixture data

Tests

• cargo test -p paimon spec::index_manifest::tests -- --nocapture

API and Format

• no public API changes
• extends index manifest metadata handling to preserve optional deletion vector cardinality when present in storage

Documentation

• N/A

[JingsongLi]

+1