fix: resolve context canceled when reading HTTP response body (#3141)

[hadzija7]

What changed

Fixes the HTTP component failing with "failed to read response body: context canceled" despite successful requests. The component now completes reading the response body before the request context is canceled.

Why

When the HTTP component made requests to endpoints that return large or slowly-streaming responses, the request context was canceled via defer cancel() immediately when executeRequest returned—before processResponse could read the body. The 30s client timeout could also fire during body read. This caused the component to fail with context canceled even when the server returned 200 OK.

Closes #3141

How

• Deferred context cancel: executeRequest now returns the cancel function to the caller instead of calling defer cancel() internally. The caller defers cancel() only after the response is fully processed.
• Error path cleanup: On error (URL parse, request creation, or Do failure), the context is canceled before returning to avoid leaking the context.
• Retry path cleanup: When scheduling a retry after a non-success status, the response body is closed before returning to avoid leaking connections.