feat: To add health status check for remote VLLM (#2303)

# What does this PR do?
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relevant issues if applicable. -->
To add health status check for remote VLLM
<!-- If resolving an issue, uncomment and update the line below -->
<!-- Closes #[issue-number] -->

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->
PR includes the unit test to test the added health check implementation
feature.

llama_stack/distribution/routers/inference.py

@@ -602,7 +602,7 @@ class InferenceRouter(Inference):
 
     async def health(self) -> dict[str, HealthResponse]:
         health_statuses = {}
-        timeout = 0.5
+        timeout = 1  # increasing the timeout to 1 second for health checks
         for provider_id, impl in self.routing_table.impls_by_provider_id.items():
             try:
                 # check if the provider has a health method