Allow duration defaults (#9249)

# Description
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Fixes #9217 (some cases, still can't accept all default expressions)

# User-Facing Changes
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- Follow-up of #8940, expanding `eval_constant` so that it can also
evaluate values with units.

# Tests + Formatting
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- A unit test was added to verify that defaults like `1sec` are
accepted.

crates/nu-parser/src/eval.rs

@@ -114,6 +114,13 @@ pub fn eval_constant(
             span: expr.span,
         }),
         Expr::Nothing => Ok(Value::Nothing { span: expr.span }),
+        Expr::ValueWithUnit(expr, unit) => {
+            if let Ok(Value::Int { val, .. }) = eval_constant(working_set, expr) {
+                Ok(unit.item.to_value(val, unit.span))
+            } else {
+                Err(ParseError::NotAConstant(expr.span))
+            }
+        }
         _ => Err(ParseError::NotAConstant(expr.span)),
     }
 }

src/tests/test_engine.rs

@@ -340,10 +340,15 @@ fn default_value12() -> TestResult {
 }
 
 #[test]
-fn default_value_constant() -> TestResult {
+fn default_value_constant1() -> TestResult {
     run_test(r#"def foo [x = "foo"] { $x }; foo"#, "foo")
 }
 
+#[test]
+fn default_value_constant2() -> TestResult {
+    run_test(r#"def foo [secs = 1sec] { $secs }; foo"#, "1sec")
+}
+
 #[test]
 fn default_value_not_constant1() -> TestResult {
     fail_test(