fix(llm-gateway): improve type safety and datetime consistency

- Add type annotations for mypy compliance
- Use UTC-aware datetimes consistently (datetime.now(UTC))
- Add type: ignore comments for LiteLLM incomplete stubs
- Fix import ordering and formatting
- Update pyproject.toml mypy configuration

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

mcp-servers/llm-gateway/providers.py

@@ -49,9 +49,9 @@ def configure_litellm(settings: Settings) -> None:
     # Configure caching if enabled
     if settings.litellm_cache_enabled:
         litellm.cache = litellm.Cache(
-            type="redis",
+            type="redis",  # type: ignore[arg-type]
             host=_parse_redis_host(settings.redis_url),
-            port=_parse_redis_port(settings.redis_url),
+            port=_parse_redis_port(settings.redis_url),  # type: ignore[arg-type]
             ttl=settings.litellm_cache_ttl,
         )
 
@@ -115,10 +115,7 @@ def _build_model_entry(
     }
 
     # Add custom base URL for DeepSeek self-hosted
-    if (
-        model_config.provider == Provider.DEEPSEEK
-        and settings.deepseek_base_url
-    ):
+    if model_config.provider == Provider.DEEPSEEK and settings.deepseek_base_url:
         entry["litellm_params"]["api_base"] = settings.deepseek_base_url
 
     return entry
@@ -269,7 +266,7 @@ class LLMProvider:
         # Create Router
         self._router = Router(
             model_list=model_list,
-            fallbacks=list(fallbacks.items()) if fallbacks else None,
+            fallbacks=list(fallbacks.items()) if fallbacks else None,  # type: ignore[arg-type]
             routing_strategy="latency-based-routing",
             num_retries=self._settings.litellm_max_retries,
             timeout=self._settings.litellm_timeout,