Type constraint violation error messages include formatting/comments from original definition

Noticed this while testing out https://github.com/apple/pkl-pantry/pull/105

The `Recur` module includes some fairly complex type constraints with comments inline for clarity, eg.
```pkl
until: (
* DateTime(
// if dtstart is defined and a datetime, until must also be a datetime if defined
dtstart?.ifNonNull((it) -> it is DateTime) ?? true,
dtstart?.ifNonNull((it) -> utc == (it as DateTime).utc) ?? true,
utc.implies(tzid == null)
)
|Date(
// if dtstart is defined and a date, until must also be a date if defined
dtstart?.ifNonNull((it) -> it is Date) ?? true,
tzid == null
)
)?
```

If non of these constraints can be satisfied, eg. by input such as
```pkl
import "@icalendar/Recur.pkl"
result = new Recur {
tzid = "America/Los_Angeles"
freq = "YEARLY"
until = DateTime.DateTime("20250101T000000Z")
}.toString()
```

Then the resulting error message will include the full original code with only newlines stripped:
```
Expected value of type `* DateTime( // if dtstart is defined and a datetime, until must also be a datetime if defined dtstart?.ifNonNull((it) -> it is DateTime) ?? true, dtstart?.ifNonNull((it) -> utc == (it as DateTime).utc) ?? true, utc.implies(tzid == null) ) |Date( // if dtstart is defined and a date, until must also be a date if defined dtstart?.ifNonNull((it) -> it is Date) ?? true, tzid == null )`, but got a different `icalendar.DateTime`. Value: new ModuleClass { date = ?; time { h = ?; m = ?; s = ?; utc = true }; utc = t...
```

Ideally this should produce output with the type/constraints [canonically formatted](https://github.com/apple/pkl-evolution/pull/15), eg. (without addition of newlines for line length)
```
Expected value of type `*DateTime(dtstart?.ifNonNull((it) -> it is DateTime) ?? true, dtstart?.ifNonNull((it) -> utc == (it as DateTime).utc) ?? true, utc.implies(tzid == null))|Date(dtstart?.ifNonNull((it) -> it is Date) ?? true, tzid == null)`, but got a different `icalendar.DateTime`. Value: new ModuleClass { date = ?; time { h = ?; m = ?; s = ?; utc = true }; utc = t...
```

Start with the Recur module and the type-constraint error path using the reproduction in the issue. Compare the current diagnostic with the canonical formatting described in pkl-evolution/pull/15; done means inline comments and source formatting no longer appear in the reported constraint type.

Written by the indexing model from the issue text.