Add OLMo2 models (1B, 7B, 13B) support to fairseq2

[YunchaoYang]

What does this PR do? Please describe:

• Add OLMo2 model architecture (1B, 7B, 13B) support in fairseq2

• The key architecture changes include:
  OLMO2 is similar to the LLaMA architecture with the following differences:

  • Olmo2RMSNorm: In Olmo2 the order of operation for RMSNorm is normalize -> multiply by weight -> cast to original dtype.
  • OLMO2TransformerLMDecoderLayer: OLMO2 uses Post-Norm in decoder layer: Attention/FFN -> Norm -> Add Residual, which is different than the existing Pre-Norm and Post-Norm order.
  • OLMO2MultiheadAttention:
    • OLMO2 adds Q/K Norm in attention layers, the Q/K has slight difference in the order of normalization and reshape: Project → Normalize → Reshape → RoPE.
    • OLMO2 MHA instead of GQA. OLMO2-32B model use GQA.
  • OLMO2RotaryEmbedding: The Rope Module reuse the existing ReferenceRotaryEncoder module.

• An integration test is added to ensure the output is consistent with HF Transformers. The integration test has passed for the 1B model.

Note:
OLMO2MultiheadAttention inherits from StandardMultiheadAttention (marked @final)
because the only difference is the order of normalization in _project_q() and _project_kv().
Reimplementing the entire class would duplicate ~150 lines of boilerplate code. Right now, the type checker warning is suppressed.

Fixes #1402

Does your PR introduce any breaking changes? If yes, please list them:
List of all backwards-incompatible changes.

Check list:

• Was the content of this PR discussed and approved via a GitHub issue? (no need for typos or documentation improvements)
• Did you read the contributor guideline?
• Did you make sure that your PR does only one thing instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests?
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (no need for typos, documentation, or minor internal changes)