[python] Update pypaimon-rust to 0.3.0

[XiaoHongbo-Hope]

Purpose

Use the published pypaimon-rust 0.3.0rc1 TestPyPI wheel in the Python 3.11 CI lane instead of building the binding from a Git revision.

This validates the release candidate as users install it and removes the no longer needed Rust toolchain setup.

Changes

• Pin pypaimon-rust 0.3.0rc1 from TestPyPI.
• Require a binary wheel and avoid dependency resolution.
• Verify the installed version and split-planning API.
• Keep the Python 3.10 lane on pypaimon-rust 0.2.0 for compatibility coverage.

Tests

• YAML parsing passed.
• git diff --check passed.
• Fork CI is running: https://github.com/XiaoHongbo-Hope/paimon/actions/runs/30073370428

[JingsongLi]

Just wait and update it to 0.3.0.