mamba2: remove hardcoded 2x expansion factor and invalid d_inner % d_state check...

mamba2: remove hardcoded 2x expansion factor and invalid d_inner % d_state check (#23082)

* mamba2: remove hardcoded 2x expansion factor, support any expand value

* mamba2: remove invalid d_inner %% d_state check (unrelated parameters)

* Update convert_hf_to_gguf.py: make expand optional with default 2

Co-authored-by: Sigbjørn Skjæret <redacted>
* mamba2: apply expand fix to refactored conversion/mamba.py

* also check for mamba_expand

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Co-authored-by: Sigbjørn Skjæret <redacted>
Co-authored-by: Sigbjørn Skjæret <redacted>