Fix HTTP connection leak when using feign.Response with chunked Transfer-Encoding

[ban-xiu]

Summary

Close #1198. When a @FeignClient method declares feign.Response as its return type and the server responds with Transfer-Encoding: chunked, the underlying HTTP connection is never released back to the connection pool, causing a connection leak.

Root Cause

Feign-core's InvocationContext.proceed() has a special path for feign.Response return type — it bypasses the entire decoder chain and calls disconnectResponseBodyIfNeeded(). This method only buffers the response body when body.length() != null && body.length() <= 8192.

For chunked responses, body.length() returns null (content length is unknown), so the buffering is skipped and the raw Response with a live InputStream tied to the pooled HTTP connection is returned directly to the caller. If the caller does not explicitly close the Response, the connection is permanently leaked.

Fix

Register a default ResponseInterceptor bean in FeignClientsConfiguration that intercepts the response before it reaches feign-core's disconnectResponseBodyIfNeeded().
When the return type is feign.Response and the body has unknown length (chunked), the interceptor:

1. Buffers the body into a byte[]
2. Closes the original response (releasing the HTTP connection)
3. Rebuilds the response with the in-memory body