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 [email protected]

• mamba2: apply expand fix to refactored conversion/mamba.py

• also check for mamba_expand

Co-authored-by: Sigbjørn Skjæret [email protected] Co-authored-by: Sigbjørn Skjæret [email protected]