fix(gguf): Add softcapping config mapping for Gemma2 and Gemma3

Add attn_logit_softcapping and final_logit_softcapping mappings
to both gemma2 and gemma3 GGUF config mappings.

Without these mappings, softcapping values are not extracted from
GGUF metadata, causing the model to use hardcoded defaults instead
of the actual values stored in the GGUF file.

Author: kitaekatt

src/transformers/integrations/ggml.py

@@ -245,6 +245,8 @@
         "attention.head_count_kv": "num_key_value_heads",
         "attention.layer_norm_rms_epsilon": "rms_norm_eps",
         "attention.sliding_window": "sliding_window",
+        "attn_logit_softcapping": "attn_logit_softcapping",
+        "final_logit_softcapping": "final_logit_softcapping",
         "vocab_size": "vocab_size",
     },
     "gemma3": {
@@ -261,6 +263,8 @@
         "attention.head_count_kv": "num_key_value_heads",
         "attention.layer_norm_rms_epsilon": "rms_norm_eps",
         "attention.sliding_window": "sliding_window",
+        "attn_logit_softcapping": "attn_logit_softcapping",
+        "final_logit_softcapping": "final_logit_softcapping",
         "vocab_size": "vocab_size",
     },
     "umt5": {