Global improvements on collaborators data

All countries 🌍

Fix: lastName, secondLastName, and birthName should be more consistently returned.
Fix: Missing end dates on collaborator contract records are now correctly populated.
Improvement: Country fields such as birthCountry and nationality are now normalized to ISO standard codes (e.g. "FR").
Improvement: Phone number values are now consistently formatted.

UK 🇬🇧

Improvement: Additional email addresses are now returned where available.
Fix: Employee matricule values were incorrect and are now fixed.