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/d45ca9107508.json

@@ -16,7 +16,7 @@
     "body": {
       "__type__": "openai.types.completion.Completion",
       "__data__": {
-        "id": "1bbb8db5-63e5-40cd-8ffe-59e0e88bf8f0",
+        "id": "rec-d45ca9107508",
         "choices": [
           {
             "finish_reason": "length",
@@ -25,7 +25,7 @@
             "text": "4. At the beginning of the year, a woman has $5,000"
           }
         ],
-        "created": 1758920353,
+        "created": 0,
         "model": "accounts/fireworks/models/llama-v3p1-8b-instruct",
         "object": "text_completion",
         "system_fingerprint": null,