feat: add HTTP migration bridges and extensible API binding

cmd/go-omni/apigen/testdata/compatibility/echo.go

@@ -0,0 +1,16 @@
+package demo
+
+import (
+	"context"
+	"example.com/compatibility/internal/types"
+)
+
+func (s *Service) Echo(ctx context.Context, req *types.EchoReq) (*types.EchoResp, error) {
+	return &types.EchoResp{ID: req.ID, Data: req.Data}, nil
+}
+func (s *Service) Item(ctx context.Context, req *types.ItemReq) (*types.EchoResp, error) {
+	return &types.EchoResp{ID: req.ID, Data: map[string]any{"found": true}}, nil
+}
+func (s *Service) Custom(ctx context.Context, req *types.CustomReq) (*types.CustomResp, error) {
+	return &types.CustomResp{Value: req.Value}, nil
+}