[python] Keep local search and lookup on one snapshot

[TheR1sing3un]

Purpose

Keep each local multimodal search execution on one snapshot. A commit between candidate search and result lookup can currently drop a selected row or return its updated values even when they violate the original pre-filter. Hybrid routes can also plan against different commits, and full-text reads lose the planning snapshot.

Capture an execution-local read view and carry it through vector, batch, full-text, hybrid, and result lookup paths. Reusing a query resolves a fresh view; explicit snapshot, tag, timestamp, and scan.version selectors remain effective. Retain resolved snapshot metadata for tags and preserve an empty view across the first concurrent commit. Share the read-view helper with existing snapshot-aware readers without mutating reusable queries or builders.

Tests

The latest full CI run passed, including Rust main 66f655b30a38: 5,204 tests passed, 121 skipped, and 2,250 native plans exercised.

• Regression coverage includes concurrent delete/update before lookup, query reuse, hybrid route planning, empty-table append, snapshot/tag/timestamp/scan.version selection, retained tag metadata, read-view copies, branch switching, full-text live-row/raw reads, and native indexed-vector lookup.
• Updated the existing PK snapshot scan test to exercise the shared table-view helper and assert that source scanning and index planning retain the same snapshot.
• After syncing with master, the snapshot, PK definitions, expanded native-planner, and incremental-read suites passed locally: 74 passed, 35 skipped (native runtime unavailable in that Python 3.9 environment). The integrated explain/profile branch also passed the broader related regression run: 399 passed, 47 skipped.
• Changed Python files pass repository-configured flake8. License-header checks and git diff --check pass.
• Full Python matrix and Rust-main validation: https://github.com/apache/paimon/actions/runs/34991660805