[python] Use native primary-key full-text search

[JingsongLi]

Purpose

Enable Native execution for the primary-key full-text searches already supported by PyPaimon, using Java's physical-position result semantics.

Depends on apache/paimon-rust#1132 reaching Rust main. Native CI continues to build main; keep this PR draft until the dependency merges.

Changes

• Send standard REST PK full-text execute_local() calls to Rust core, retaining the existing FAST-only contract and propagating execution errors without a Python retry.
• Reuse one metadata converter for Native PK vector and full-text results. Core owns snapshot selection, query execution, Top-K, score alignment and selected file ranges; Python converts the captured result.
• Use Java-compatible BinaryRow serialization for Python search-position partitions. The previous repr(tuple(...)) form disagreed with both Java and Rust and changed the cross-partition tie breaker. No compatibility path is retained.

Verification

• 422 Native cases passed across full-text, PK full-text, vector and hybrid regression suites (421 in the combined run plus the additional delayed-read test).
• 59 original Python tests passed, plus 7 subtests.
• The new 38-case REST suite copies the existing Java PK full-text golden data and compares Python/Native historical snapshots, physical positions, BM25 scores, selected splits and materialized rows.
• Tests cover projection/zero projection, reusable captured plans and readers, context mismatches, FAST-only errors and no Python retry after Native failures. Temporarily moving user Parquet files still permits index search; only reading user columns fails.
• Nonempty/empty GenericRow and BinaryRow partitions now agree, and PK vector tests also compare partition bytes.
• Rebuilt the final extension; its 8 vector binding tests and 39 final PK/DE full-text smoke cases passed.
• Flake8, license headers and Python 3.6 syntax checks passed.

The production adapter changes remain small; the query implementation is in the companion Rust core PR.

[leaves12138]

Reviewed the native primary-key full-text path against the Java implementation and the merged Rust dependency (#1132). The Python changes correctly preserve FAST-only behavior, snapshot-scoped physical positions, deletion vectors, serialized splits, score ordering, and the shared PK result conversion. No blocking code issues found. The failing Native CI was built before Rust #1132 reached main, and the Python 3.6 failure is an unrelated Debian archive dependency 404.