0522ae8155
When no custom resolver or host mapper is configured, xnet.Resolve now resolves hostnames via Go's native pure-Go resolver (PreferGo: true) instead of returning the hostname unchanged. Previously, the unresolved hostname would reach net.Dialer.DialContext, which on CGO_ENABLED=1 builds used cgo-based DNS — blocking a dedicated OS thread per concurrent lookup. At scale (1000+ listeners), this exhausted Go's 10000-thread limit. Fixes go-gost/gost#550