fix(registry): log Unregister Close errors, add doc comments and 59 unit tests

Log close errors in Unregister instead of silently discarding them.
Add doc comments to all exported symbols across 20 registry files.
Add comprehensive tests covering base registry, all wrapper types,
hot-reload delegation, nil-fallback semantics, and global accessors.

registry/dialer.go

@@ -5,12 +5,18 @@ import (
 	"github.com/go-gost/core/logger"
 )
 
+// NewDialer is a factory function that creates a new dialer.Dialer
+// from the given options.
 type NewDialer func(opts ...dialer.Option) dialer.Dialer
 
+// dialerRegistry stores dialer factory functions. Duplicate registrations
+// are treated as fatal errors (logger.Default().Fatal).
 type dialerRegistry struct {
 	registry[NewDialer]
 }
 
+// Register stores a dialer factory under the given name. Calls Fatal on
+// duplicate registration since dialer names must be unique at init time.
 func (r *dialerRegistry) Register(name string, v NewDialer) error {
 	if err := r.registry.Register(name, v); err != nil {
 		logger.Default().Fatal(err)