move out tracers

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

tracer/noop.go

@@ -0,0 +1,25 @@
+package tracer
+
+import "context"
+
+type noop struct{}
+
+func (n *noop) Init(...Option) error {
+	return nil
+}
+
+func (n *noop) Start(ctx context.Context, name string) (context.Context, *Span) {
+	return nil, nil
+}
+
+func (n *noop) Finish(*Span) error {
+	return nil
+}
+
+func (n *noop) Read(...ReadOption) ([]*Span, error) {
+	return nil, nil
+}
+
+func newTracer(opts ...Option) Tracer {
+	return &noop{}
+}