docs: add example notebooks for rate limiting, file search, and caching model

- 18-rate-limiting.ipynb: RedisRateLimitGuardrail with sliding/fixed windows
- 19-file-search-tool.ipynb: RedisFileSearchTool with HybridSearchService
- 20-caching-model.ipynb: RedisCachingModel wrapping the SDK Model interface
- Add test-all Makefile target for running API tests

Author: Brian Sam-Bodden

Makefile

@@ -9,6 +9,9 @@ install:  ## Install dependencies with uv
 test:  ## Run tests
 	uv run pytest -v
 
+test-all:  ## Run all tests including API tests
+	uv run pytest --run-api-tests -v
+
 test-cov:  ## Run tests with coverage
 	uv run pytest --cov=src --cov-report=html --cov-report=term