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/max_parallel_test.go

@@ -0,0 +1,66 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package runner
+
+import (
+	"testing"
+
+	"gitea.dev/actionslib/pkg/model"
+	"github.com/stretchr/testify/assert"
+	"go.yaml.in/yaml/v4"
+)
+
+func TestMaxParallelStrategy(t *testing.T) {
+	tests := []struct {
+		name                string
+		maxParallelString   string
+		expectedMaxParallel int
+	}{
+		{
+			name:                "max-parallel-1",
+			maxParallelString:   "1",
+			expectedMaxParallel: 1,
+		},
+		{
+			name:                "max-parallel-2",
+			maxParallelString:   "2",
+			expectedMaxParallel: 2,
+		},
+		{
+			name:                "max-parallel-default",
+			maxParallelString:   "",
+			expectedMaxParallel: 4,
+		},
+		{
+			name:                "max-parallel-10",
+			maxParallelString:   "10",
+			expectedMaxParallel: 10,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matrix := map[string][]any{
+				"version": {1, 2, 3, 4, 5},
+			}
+
+			var rawMatrix yaml.Node
+			err := rawMatrix.Encode(matrix)
+			assert.NoError(t, err) //nolint:testifylint // pre-existing issue from nektos/act
+
+			job := &model.Job{
+				Strategy: &model.Strategy{
+					MaxParallelString: tt.maxParallelString,
+					RawMatrix:         rawMatrix,
+				},
+			}
+
+			matrixes, err := job.GetMatrixes()
+			assert.NoError(t, err) //nolint:testifylint // pre-existing issue from nektos/act
+			assert.NotNil(t, matrixes)
+			assert.Len(t, matrixes, 5)
+			assert.Equal(t, tt.expectedMaxParallel, job.Strategy.MaxParallel)
+		})
+	}
+}