feat: experiments logging improvements (#2049)

* feat: warn when enabling inactive experiments

* feat: TASK_ environment prefix

* feat: calculate experiment enabled/active instead of storing

* refactor: rename GetTaskVar to GetTaskEnv

* feat: experiments tests

internal/env/env.go

@@ -8,6 +8,8 @@ import (
 	"github.com/go-task/task/v3/taskfile/ast"
 )
 
+const taskVarPrefix = "TASK_"
+
 func Get(t *ast.Task) []string {
 	if t.Env == nil {
 		return nil
@@ -23,7 +25,7 @@ func GetFromVars(env *ast.Vars) []string {
 		if !isTypeAllowed(v) {
 			continue
 		}
-		if !experiments.EnvPrecedence.Enabled {
+		if !experiments.EnvPrecedence.Enabled() {
 			if _, alreadySet := os.LookupEnv(k); alreadySet {
 				continue
 			}
@@ -42,3 +44,7 @@ func isTypeAllowed(v any) bool {
 		return false
 	}
 }
+
+func GetTaskEnv(key string) string {
+	return os.Getenv(taskVarPrefix + key)
+}