message: impl UnpackValue for StringValue
  Summary: So `StringValue` can be used as native function parameter.
diff: @@ -33,7 +33,7 @@ use gazebo::{
  use crate::values::{
  layout::{arena::AValueRepr, avalue::VALUE_STR_A_VALUE_PTR, value::FrozenValue},
  string::StarlarkStr,
  - Freezer, Trace, Tracer, Value,
  + Freezer, Trace, Tracer, UnpackValue, Value,
  };
  /// A constant string that can be converted to a [`FrozenValue`].
  @@ -260,6 +260,12 @@ unsafe impl<'v> Trace<'v> for StringValue<'v> {
  }
  }
  +impl<'v> UnpackValue<'v> for StringValue<'v> {
  + fn unpack_value(value: Value<'v>) -> Option<Self> {
  + StringValue::new(value)
  + }
  +}
  +
  /// Create a [`FrozenStringValue`].
  #[macro_export]
  macro_rules! const_frozen_string {
  