undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent

### Impact undici's `Agent` passes its constructor options through a JSON-based deep clone (`JSON.parse(JSON.stringify(...))`) before forwarding them to each per-origin `Pool`. JSON cannot represent functions, so a caller-supplied `tls` option containing a `checkServerIdentity` callback is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom `checkServerIdentity` was written to reject, but which passes Node's default hostname and chain checks, is silently accepted when the request is made through `Agent`. Because `Agent` is the default dispatcher behind `request`, `fetch`, and `setGlobalDispatcher`, this is the path most applications use. `EnvHttpProxyAgent` is also affected on its direct and `NO_PROXY` routes, which delegate to an internal `Agent`. Only applications that pass a function-valued `tls` option (such as a custom `checkServerIdentity` for certificate or public-key pinning) are affected. Passing the same options through `connect` is not affected. This is the `Agent` counterpart of the `BalancedPool` certificate validation bypass fixed in CVE-2026-84961. ### Patches Upgrade to undici `6.29.1`, `7.30.1`, or `8.12.2`. `Agent` now preserves the `tls` option outside the JSON clone, so custom TLS verification callbacks are forwarded to each origin unchanged. ### Workarounds Pass the TLS options through `connect` instead of `tls`. For proxied `EnvHttpProxyAgent` destinations, use `requestTls` / `proxyTls`.