refactor: taskfile/ast package (#1450)

* refactor: ast package

* feat: read -> taskfile

* refactor: taskfile.Taskfile -> taskfile.Read

* refactor: move merge function back into taskfile package

* refactor: rename taskfile.go to read.go

taskfile/ast/precondition_test.go

@@ -0,0 +1,51 @@
+package ast_test
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/yaml.v3"
+
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+func TestPreconditionParse(t *testing.T) {
+	tests := []struct {
+		content  string
+		v        any
+		expected any
+	}{
+		{
+			"test -f foo.txt",
+			&ast.Precondition{},
+			&ast.Precondition{Sh: `test -f foo.txt`, Msg: "`test -f foo.txt` failed"},
+		},
+		{
+			"sh: '[ 1 = 0 ]'",
+			&ast.Precondition{},
+			&ast.Precondition{Sh: "[ 1 = 0 ]", Msg: "[ 1 = 0 ] failed"},
+		},
+		{
+			`
+sh: "[ 1 = 2 ]"
+msg: "1 is not 2"
+`,
+			&ast.Precondition{},
+			&ast.Precondition{Sh: "[ 1 = 2 ]", Msg: "1 is not 2"},
+		},
+		{
+			`
+sh: "[ 1 = 2 ]"
+msg: "1 is not 2"
+`,
+			&ast.Precondition{},
+			&ast.Precondition{Sh: "[ 1 = 2 ]", Msg: "1 is not 2"},
+		},
+	}
+	for _, test := range tests {
+		err := yaml.Unmarshal([]byte(test.content), test.v)
+		require.NoError(t, err)
+		assert.Equal(t, test.expected, test.v)
+	}
+}