Add func definitions for resolver and tracer

This adds some basic convenience types to make working with these
new types and abstractions easier.

resolver/resolver.go

@@ -16,6 +16,20 @@ type Resolver interface {
 	isResolver()
 }
 
+// ResolverFunc is a convenience type that implements the [Resolver] abstraction.
+//
+// This enables using normal function definitions to handle custom resolution.
+type ResolverFunc func(context.Context, string) (any, error)
+
+// Resolve calls the underlying function to resolve the reference.
+func (f ResolverFunc) Resolve(ctx context.Context, reference string) (any, error) {
+	return f(ctx, reference)
+}
+
+func (ResolverFunc) isResolver() {}
+
+var _ Resolver = (*ResolverFunc)(nil)
+
 // NoopResolver is a Resolver that does nothing.
 type NoopResolver struct {
 	BaseResolver

tracer/tracer.go

@@ -21,6 +21,16 @@ type Tracer interface {
 	Trace(name string, collection collection.Collection) error
 }
 
+// TracerFunc is a convenience type that implements the [Tracer] abstraction.
+//
+// This enables using normal function definitions to handle custom tracing.
+type TracerFunc func(string, collection.Collection) error
+
+// Trace calls the underlying function to trace the collection.
+func (f TracerFunc) Trace(name string, collection collection.Collection) error {
+	return f(name, collection)
+}
+
 // NoopTracer is a Tracer that does nothing.
 type NoopTracer struct{}