ax(mining): replace prose comment on WithDefaults with usage example

AX Principle 2: comments show HOW with real values, not what the signature already says.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/repository.go

@@ -32,7 +32,7 @@ type FileRepository[T any] struct {
 // FileRepositoryOption configures a FileRepository.
 type FileRepositoryOption[T any] func(*FileRepository[T])
 
-// WithDefaults sets the default value factory for when the file doesn't exist.
+// repo := NewFileRepository[MinersConfig](path, WithDefaults(defaultMinersConfig))
 func WithDefaults[T any](fn func() T) FileRepositoryOption[T] {
 	return func(r *FileRepository[T]) {
 		r.defaults = fn