Fix shape error that occurred when loading lora weight of gemma2 model.

[upskyy]

Motivation & Modifications

The get_hidden_dim functions of the llama model and the gemma2 model differ, which causes a shape error when loading gemma2 lora weights.
For example, in the llama model, head_dim * num_attention_heads equals hidden_size, so using self.config.hidden_size, self.config.hidden_size works fine. (3072 = 128 * 24)
However, in the gemma2 model, head_dim * num_attention_heads and hidden_size are unrelated and need to be implemented differently. Specifically, in the gemma2 model, hidden_size is 2304, while head_dim * num_attention_heads is 2048. (2304 != 2048)

As a result, the q_proj in the gemma2 model should be defined as self.config.hidden_size, self.config.head_dim * self.config.num_attention_heads rather than self.config.hidden_size, self.config.hidden_size.
Since the input_dim and output_dim are different, the o_proj also needs to be adjusted.
I modified the code to ensure that the gemma2 model works correctly with multi-LoRA inference, and I have verified its functionality.

llama3 config : https://huggingface.co/meta-llama/Llama-3.2-3B-Instruct/blob/main/config.json
gemma2 config : https://huggingface.co/google/gemma-2-2b-it/blob/main/config.json
current get_hidden_dim functions : https://github.com/sgl-project/sglang/blob/v0.3.6.post2/python/sglang/srt/models/llama.py#L326-L339

The gemma2 model does not have a get_hidden_dim function implemented, which allows it to bypass the following code
(https://github.com/sgl-project/sglang/blob/v0.3.6.post2/python/sglang/srt/lora/lora_manager.py#L34-L46)

Checklist

• Format your code according to the Contributor Guide.
• Add unit tests as outlined in the Contributor Guide.
• Update documentation as needed, including docstrings or example tutorials.