refactor: move act under internal

The runner is an application, not a library. `act/model` and
`act/exprparser` were the last packages anything outside this repository
consumed and they now live in actionslib, so nothing needs the rest of
`act` to be importable, and keeping it importable invites the coupling
that was just removed.

Import paths only, the files are unchanged.

Assisted-by: Codet:GPT-5.1-Codex

internal/act/runner/step_factory.go

@@ -0,0 +1,50 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Copyright 2022 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"fmt"
+
+	"gitea.dev/actionslib/pkg/model"
+)
+
+type stepFactory interface {
+	newStep(step *model.Step, rc *RunContext) (step, error)
+}
+
+type stepFactoryImpl struct{}
+
+func (sf *stepFactoryImpl) newStep(stepModel *model.Step, rc *RunContext) (step, error) {
+	switch stepModel.Type() {
+	case model.StepTypeInvalid:
+		return nil, fmt.Errorf("Invalid run/uses syntax for job:%s step:%+v", rc.Run, stepModel)
+	case model.StepTypeRun:
+		return &stepRun{
+			Step:       stepModel,
+			RunContext: rc,
+		}, nil
+	case model.StepTypeUsesActionLocal:
+		return &stepActionLocal{
+			Step:       stepModel,
+			RunContext: rc,
+			readAction: readActionImpl,
+			runAction:  runActionImpl,
+		}, nil
+	case model.StepTypeUsesActionRemote:
+		return &stepActionRemote{
+			Step:       stepModel,
+			RunContext: rc,
+			readAction: readActionImpl,
+			runAction:  runActionImpl,
+		}, nil
+	case model.StepTypeUsesDockerURL:
+		return &stepDocker{
+			Step:       stepModel,
+			RunContext: rc,
+		}, nil
+	}
+
+	return nil, fmt.Errorf("Unable to determine how to run job:%s step:%+v", rc.Run, stepModel)
+}