Cast MagicLink's UUID to a string when initially set

[rossbearman]

Resolves #112.

[rossbearman]

The failing PHPStan test is unrelated to this change.

[cesargb]

@rossbearman Its true, the fail with PhpStan is not related with this PR.

[cesargb]

@rossbearman Can your reopen this change?

[rossbearman]

Hi @cesargb, I realised the issue wasn't directly related to laravel-magiclink. The failure was only happening at my end because declare(strict_types=1); was being injected everywhere by a rogue Pint configuration.

The issue isn't present after pulling in a clean version of the package, as LazyUuidFromString gets cast automatically when declare(strict_types=1); isn't present.