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/container/executions_environment.go

@@ -0,0 +1,19 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Copyright 2022 The nektos/act Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package container
+
+import "context"
+
+type ExecutionsEnvironment interface {
+	Container
+	ToContainerPath(string) string
+	GetActPath() string
+	GetPathVariableName() string
+	DefaultPathVariable() string
+	JoinPathVariable(...string) string
+	GetRunnerContext(ctx context.Context) map[string]any
+	// On windows PATH and Path are the same key
+	IsEnvironmentCaseInsensitive() bool
+}