This simplifies PING call during the initialisation, to pass no parameters and expect the default response.

Why?

My motivation for this change is to enable support of Redis under Envoy proxy:

• Envoy doesn't support PING with parameters and Triton fails to initialise the cache (error: creating server: Internal - Failed to initialise RedisCache: Failed to ping Redis server.)
• Standard Redis PING response without parameter is PONG - that's how Envoy Redis also behaves.
• This increases cache compatibility with a very minimal change to initialisation.

Testing

I performed some manual tests to verify this change behaves as expected:

• built binary on Mac inside Docker container
• loaded into Triton Server as a custom cache
• tested SigLIP2 model calls on locally running regular Redis container
• tested SigLIP2 model calls on Envoy Redis
• In both cases verified that the cache is being used