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/c8a59b661fd5.json

@@ -16,7 +16,7 @@
     "body": {
       "__type__": "openai.types.completion.Completion",
       "__data__": {
-        "id": "oCfwct8-4Yz4kd-984c2861287d4cc3",
+        "id": "rec-c8a59b661fd5",
         "choices": [
           {
             "finish_reason": "length",
@@ -26,7 +26,7 @@
             "seed": 12050749903881546000
           }
         ],
-        "created": 1758820465,
+        "created": 0,
         "model": "meta-llama/Llama-3.3-70B-Instruct-Turbo-Free",
         "object": "text.completion",
         "system_fingerprint": null,