refactor(hand): rename L25 and O30i models to L20 and O30

[zhuzx17]

Summary

• Rename the L25 hand model to L20.
• Rename the O30i hand model to O30.
• Update module paths, exports, documentation, examples, tests, and pytest markers.
• Remove all L25 and O30i compatibility aliases and legacy package paths.
• Require users to create instances through the L20 and O30 APIs only.
• Update the unreleased changelog.

Validation

• Targeted tests: 144 passed.
• Full non-hardware tests: 865 passed.
• uv build passed.
• Ruff checks and formatting passed for changed Python files.