refactor: migrate Slime MUSA bootstrap to musa_titan - #2398

Summary

Migrate Slime's MUSA accelerator bootstrap from the legacy musa_patch dependency to musa_titan.

Changes

• Replace musa_patch imports and state tracking with musa_titan.
• Replace MUSA_PATCH_PATH with MUSA_TITAN_PATH.
• Invoke musa_titan.apply_rl_patch() during MUSA accelerator initialization.
• Keep compatibility with patch_after_import_torch() for older musa_titan interfaces.
• Update the MUSA accelerator implementation and accelerator unit tests.
• Preserve accelerator initialization before importing SGLang submodules.

Scope

Only the musa_titan migration commit is included.