[evaluation] Generation mode and videomme benchmark support for Gemma4

[Torrero]

This PR adds generation support and Video-MME benchmark support to the Gemma4 PTQ wrappers:

1. Generation support — QuantGemma4ForCausalLM and QuantGemma4ForConditionalGeneration now inherit from GenerationMixin and implement all the methods HF's generate().

2. Video-MME benchmark support — The Gemma4 adapter's evaluate() method now support videomme benchmark.
   For gemma4 evaluation with max_position_embeddings=2048 we should use max_num_frames = 21 unlike qwen3-vl where max_num_frames=35 is used.
   In Gemma4, the minimum limit of soft_tokens_per_frame=70 (comes from processor.video_processor.max_soft_tokens) when for qwen3-vl we can control the minimum tokens per frame.

**The formula:**

input_budget     = max_position_embeddings - max_new_tokens - safety_margin
visual_budget    = input_budget - text_token_margin
max_num_frames   = visual_budget // soft_tokens_per_frame


max_position_embeddings=2048
max_new_tokens=30
safety_margin=4
text_token_margin=512
soft_tokens_per_frame=70 

**The arithmetic:**

input_budget  = 2048 - 30 - 4      = 2014
visual_budget = 2014 - 512          = 1502
max_num_frames = 1502 / 70        = 21

Co-Authored-By: Cline

TICO-DCO-1.0-Signed-off-by: Evgenii Maltsev e.maltsev@samsung.com

[mhs4670go]

LGTM