Consolidate tests/client-sdk and providers/tests

[yanxi0830]

🚀 Describe the new functionality needed

• See prerequisite issue in: https://github.com/meta-llama/llama-stack/issues/651

Why

• We currently use providers/tests (to test impls) and tests/client-sdk to test SDK (via directClient & httpClient)
• We don't want to maintain 2 sets of tests and consolidate to a single suite of tests

What

• Audit existing tests on functionalities in providers/tests
• Merge providers/tests with tests/client-sdk

Code Pointer

• tests/client-sdk: https://github.com/meta-llama/llama-stack/tree/main/tests/client-sdk
• providers/tests: https://github.com/meta-llama/llama-stack/tree/main/llama_stack/providers/tests

💡 Why is this needed? What if we don't build it?

Reliability

Other thoughts

No response