Standard Library serialization and deserialization error

[MikaelMayer]

Dafny version

latest-nightly

Code to produce this issue

@Test
  method SpecTest() {
    expect Std.JSON.Spec.EscapeUnicode(7) == "0007";
  }

Command to run and resulting output

dafny test on that code when importing the standard libraries
It returnes `"7   "` instead which is an error.
Also, putting an escape like `\u0007` at the end of a string literal fails to deserialize

What happened?

Needs to be fixed

What type of operating system are you experiencing the problem on?

Windows

[MikaelMayer]

fixed by #6228