[JingsongLi]

Purpose

Fix native index compatibility failures reported by Paimon Native CI. Existing PK vector payloads can use a different metric from the current schema, and portable build requests can contain opaque implementation parameters.

Brief change log

• Use the first nonempty captured ANN payload's metric for indexed scoring, exact fallback and refinement. Validate every searched payload header against that metric, and retain table metrics for raw-only plans.
• Reuse the vector metadata/header reader for bucket-local payloads without serializing header reads across all segments.
• Pass recognized generic build parameters to strict native validation while retaining opaque options in captured plans. Known invalid or implementation-incompatible parameters still fail.
• Cover empty segments, mixed metrics, captured sources, and single/batch/refined searches over indexed and raw data.

Tests

• 59 focused Rust unit tests across PK vector reads, vector search/options and generic index builds.
• 2 Java-fixture integration tests.
• cargo +1.98.0 fmt --all -- --check.
• cargo +1.98.0 clippy --locked -p paimon --lib --tests -- -D warnings.

API and Format

No API signature or storage-format changes. Generic builds ignore opaque implementation parameters consistently with Java/PyPaimon; the low-level strict options API is unchanged.

Documentation

No new configuration options.

[leaves12138]

LGTM