fix: close failed ping response bodies

[bensynapse]

I run Live Tennis API.

HTTP retries leave discarded response bodies open. Failed pings also return before closing the final response, so repeated failures retain connections.

Close discarded responses before retrying. Keep the final response available to Post callers, and close it in ping on success or failure.

Seven regression cases fail before the fix. They cover successful retries, exhausted retries and permanent errors, with controls for successful responses and direct Post callers.

go test -race ./..., ./scripts/build and go vet ./... pass on Go 1.27.0. Formatting is clean.
The built client also passes three HTTP scenarios in the project's Docker image, including retry payloads and connection cleanup.

[bdd]

Thank you

[bdd]

Expect a new release by Oct 1.