Go: implement ASR in ZhipuAI driver (#15134)

### What problem does this PR solve?

This PR implements ASR and TTS support for the ZhipuAI Go driver.

The ZhipuAI model config already advertises `glm-asr-2512` as an ASR
model, but the Go driver returned `zhipu, no such method` from
`TranscribeAudio`. This adds the documented audio transcription endpoint
suffix and sends multipart transcription requests with `model`,
`stream=false`, and `file` fields.

Per maintainer review, this also adds the ZhipuAI TTS endpoint suffix
and implements `AudioSpeech` / `AudioSpeechWithSender` for `glm-tts`.

Closes #15133

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)

conf/models/zhipu-ai.json

@@ -9,6 +9,8 @@
     "async_result": "async-result",
     "embedding": "embeddings",
     "rerank": "rerank",
+    "asr": "audio/transcriptions",
+    "tts": "audio/speech",
     "files": "files",
     "models": "models"
   },
@@ -268,4 +270,4 @@
       ]
     }
   ]
-}
+}