[python] Integrate native REST authorization casts

[JingsongLi]

Purpose

Integrate the Java-compatible REST authorization CAST implementation already merged in apache/paimon-rust#1125 into Python Native reads. CAST and authorization expression execution remain in Rust.

Changes

• Preserve the physical read type while making masked output fields nullable according to the captured grant, including NOT NULL targets, named projections, empty plans and batch readers.
• Preserve field and schema metadata when producing masked or projected output.
• Add compact Native integration tests across append, primary-key and data-evolution tables. The tests prohibit Python authorization expression execution and Python read/scan fallback.
• Cover representative numeric, decimal, text, binary and temporal CASTs, rebinding, authorization short circuiting, hidden columns, filter/limit ordering, exact output storage and invalid runtime classes.
• Cover Native schema evolution from Parquet LargeUtf8 to INT.
• Keep the process timezone unchanged in tests and exercise Native authorization/temporal CASTs in separate Shanghai and New York processes in CI, with system tzdata installed.

The PR is limited to five files: 29 production insertions and eight deletions, 319 test lines and a Native CI timezone regression step. The duplicated Python CAST implementation and large Java-vector fixtures have been removed. The full Java capability matrix and reference vectors live in the merged Rust PR.

Verification

• Compact Native integration suite and existing Native authorization tests before adding three timezone cases: 226 passed.
• Dedicated Native CAST and temporal regressions: 55 passed per process in UTC, Asia/Shanghai and America/New_York.
• Additional Native LargeUtf8 schema-evolution regression: passed.
• Python predicate/authorization/evolution/projection tests: 515 passed, 2,127 subtests.
• Existing reader/evolution/projection regressions: 91 passed, 23 subtests.
• Python 3.6 compatibility test directory under the local Python 3.13 runtime: 79 passed.
• Numeric utility and split serialization regressions: 68 passed, 14 subtests.
• Flake8, Apache license headers, Python 3.6 syntax and diff checks passed.
• Independent review reproduced all 41 representative CAST expectations against Java and found no differences.

Native CI continues to build paimon-rust main; no fork or PR revision is pinned.

[leaves12138]

Reviewed the latest head 461b1e6. I found no blocking issues. The Python changes correctly keep native authorization execution in Rust and only adapt output nullability, field/schema metadata, projections, and native schema-evolution wiring. Verification passed: Rust binding built from paimon-rust#1125 head c747879; native CAST and schema-evolution tests passed 361/361 with TZ=UTC; adjacent Python authorization, projection, and schema-validation regressions passed 301/301; Python syntax and diff checks passed. The single GitHub Actions check was still queued when this review was submitted.