chore(tests): normalize recording IDs and timestamps to reduce git diff noise (#3676)

IDs are now deterministic hashes based on request content, and
timestamps are normalized to constants, eliminating spurious changes
when re-recording tests.

## Changes
- Updated `inference_recorder.py` to normalize IDs and timestamps during
recording
- Added `scripts/normalize_recordings.py` utility to re-normalize
existing recordings
- Created documentation in `tests/integration/recordings/README.md`
- Normalized 350 existing recording files

tests/integration/recordings/responses/b44cc7a7afc8.json

@@ -20,11 +20,11 @@
       "__type__": "ollama._types.EmbedResponse",
       "__data__": {
         "model": "all-minilm:l6-v2",
-        "created_at": null,
+        "created_at": "1970-01-01T00:00:00.000000Z",
         "done": null,
         "done_reason": null,
-        "total_duration": 105611084,
-        "load_duration": 42126542,
+        "total_duration": 0,
+        "load_duration": 0,
         "prompt_eval_count": 162,
         "prompt_eval_duration": null,
         "eval_count": null,