refactor: unify interleaved MRoPE rotary embedding

[CUHKSZzxy]

Summary

• unify MRoPE rotary table generation so Qwen3-VL interleaved MRoPE and Qwen2-style chunked MRoPE share the backend rotary embedding path
• keep text-only position ids on the regular RoPE path
• add focused coverage for chunked MRoPE, interleaved MRoPE, YaRN MRoPE overrides, and text-position fallback
• remove the MRoPE position-id padding helper and its dedicated test case

Validation

• focused rotary embedding unit tests passed

Assistance

Assisted with Codex + GPT-5.5 xHigh Fast