Add Cohere2 architecture adapter

[hsusul]

Summary

Addresses #1474

Adds TransformerBridge support for Cohere2ForCausalLM, including Cohere Command-R7B / Command-A style interleaved attention.

The adapter extends the existing Cohere support and handles both Cohere2 interleave encodings:

• explicit layer_types
• sliding_window_pattern / _sliding_window_pattern

Sliding-window layers retain RoPE, while full-attention layers suppress RoPE / use NoPE behavior.

Tests

• Cohere2 unit tests + registry sync: 23 passed
• Existing Cohere unit tests: 55 passed
• Tiny Cohere2 integration test: 5 passed
• Combined Cohere2 unit + integration rerun: 24 passed
• black --check
• isort --check-only
• targeted mypy
• git diff --check