This PR updates the email validation regex to better handle use cases
with hyphens.
Changes:
- Disallows domains starting or ending with a hyphen
(`user@-example.com`, `user@example-.com`).
- Allows domains with consecutive hyphens inside (`user@ex--ample.com`).
- Allows multiple subdomains (`user@sub.domain.example.com`).
- Adds `int test` coverage for multiple domain use case scenarios.
afe443267d