feat(tests): auto-merge all model list responses and unify recordings (#3320)

One needed to specify record-replay related environment variables for
running integration tests. We could not use defaults because integration
tests could be run against Ollama instances which could be running
different models. For example, text vs vision tests needed separate
instances of Ollama because a single instance typically cannot serve
both of these models if you assume the standard CI worker configuration
on Github. As a result, `client.list()` as returned by the Ollama client
would be different between these runs and we'd end up overwriting
responses.

This PR "solves" it by adding a small amount of complexity -- we store
model list responses specially, keyed by the hashes of the models they
return. At replay time, we merge all of them and pretend that we have
the union of all models available.

## Test Plan

Re-recorded all the tests using `scripts/integration-tests.sh
--inference-mode record`, including the vision tests.

docs/source/contributing/testing/record-replay.md

@@ -40,18 +40,15 @@ The system patches OpenAI and Ollama client methods to intercept calls before th
 
 ### Storage Architecture
 
-Recordings use a two-tier storage system optimized for both speed and debuggability:
+Recordings are stored as JSON files in the recording directory. They are looked up by their request hash.
 
 ```
 recordings/
-├── index.sqlite          # Fast lookup by request hash
 └── responses/
     ├── abc123def456.json  # Individual response files
     └── def789ghi012.json
 ```
 
-**SQLite index** enables O(log n) hash lookups and metadata queries without loading response bodies.
-
 **JSON files** store complete request/response pairs in human-readable format for debugging.
 
 ## Recording Modes
@@ -166,8 +163,8 @@ This preserves type safety - when replayed, you get the same Pydantic objects wi
 Control recording behavior globally:
 
 ```bash
-export LLAMA_STACK_TEST_INFERENCE_MODE=replay
-export LLAMA_STACK_TEST_RECORDING_DIR=/path/to/recordings
+export LLAMA_STACK_TEST_INFERENCE_MODE=replay   # this is the default
+export LLAMA_STACK_TEST_RECORDING_DIR=/path/to/recordings   # default is tests/integration/recordings
 pytest tests/integration/
 ```