[JingsongLi]

Purpose

Fix the Python side of the Native CI failures.

Keep explicit global-index build options separate from table defaults so an alias in a build request can override a different alias in the schema. Apply None as removal of a schema default and preserve Python's typed integer conversion for build parallelism before crossing the string-only ABI. Index option resolution remains in Rust.

Update regression tests to inspect the actual copied table, retain captured snapshots, check typed/default controls and source precedence, and use training-only invalid parameters to verify that all-null shards skip training.

Companion Rust fix: apache/paimon-rust#1270. Native CI builds apache/paimon-rust@main, so merge the companion Rust PR first. Local native validation uses both patched repositories.

Tests

• 99 Python option/build tests passed, with 48 subtests.
• 421 native integration tests passed across index-result scans, parallel builds, captured snapshots/plans, vector index builds and vector search, with native planning/reading/writing/committing enabled.
• Changed Python files pass Flake8.
• Python license-header check passes for all 1256 files.

[leaves12138]

LGTM