chore: move the experiments package out of the internal/ dir

Closes #2014

experiments/experiment.go

@@ -0,0 +1,67 @@
+package experiments
+
+import (
+	"fmt"
+	"slices"
+	"strconv"
+
+	"github.com/go-task/task/v3/taskrc/ast"
+)
+
+type Experiment struct {
+	Name          string // The name of the experiment.
+	AllowedValues []int  // The values that can enable this experiment.
+	Value         int    // The version of the experiment that is enabled.
+}
+
+// New creates a new experiment with the given name and sets the values that can
+// enable it.
+func New(xName string, config *ast.TaskRC, allowedValues ...int) Experiment {
+	var value int
+	if config != nil {
+		value = config.Experiments[xName]
+	}
+
+	if value == 0 {
+		value, _ = strconv.Atoi(getEnv(xName))
+	}
+
+	x := Experiment{
+		Name:          xName,
+		AllowedValues: allowedValues,
+		Value:         value,
+	}
+	xList = append(xList, x)
+	return x
+}
+
+func (x Experiment) Enabled() bool {
+	return slices.Contains(x.AllowedValues, x.Value)
+}
+
+func (x Experiment) Active() bool {
+	return len(x.AllowedValues) > 0
+}
+
+func (x Experiment) Valid() error {
+	if !x.Active() && x.Value != 0 {
+		return &InactiveError{
+			Name: x.Name,
+		}
+	}
+	if !x.Enabled() && x.Value != 0 {
+		return &InvalidValueError{
+			Name:          x.Name,
+			AllowedValues: x.AllowedValues,
+			Value:         x.Value,
+		}
+	}
+	return nil
+}
+
+func (x Experiment) String() string {
+	if x.Enabled() {
+		return fmt.Sprintf("on (%d)", x.Value)
+	}
+	return "off"
+}