GHSA-79qm-7rj5-m7r9

### Summary

The Proxy Helper (`hono/proxy`) does not remove response headers named by the origin's `Connection` header. Headers that the origin marked as connection-scoped are therefore forwarded to clients.

### Details

Per RFC 9110 Section 7.6.1, an intermediary must remove the header fields listed in a message's `Connection` header field before forwarding the message, in addition to the well-known hop-by-hop headers. The `proxy()` function removed the well-known hop-by-hop headers (including `Connection` itself) from origin responses, but did not remove the headers that the response's `Connection` header field designated as connection-scoped.

This issue arises when an application proxies responses from an origin that declares additional, non-standard headers as hop-by-hop via the `Connection` response header.

### Impact

A client may receive response headers that the origin intended only for its immediate peer. This may lead to:

- Disclosure of connection-scoped or internal metadata contained in such headers

This issue affects applications that use the Proxy Helper (`hono/proxy`) to forward responses from origins that list custom header names in their `Connection` response header. Applications whose origins only use the standard hop-by-hop headers are not affected.