Add support for doctrine/collections 3.x

[a-treschilov]

Summary

• Extends the doctrine/collections version constraint from ^1.6.8 || ^2.0 to ^1.6.8 || ^2.0 || ^3.0
• No code changes required — GrumPHP's collection classes only use core ArrayCollection methods that remain fully compatible in 3.x
• doctrine/collections 3.0.0 requires PHP 8.4+, so Composer's platform resolution automatically selects 3.x on PHP 8.4/8.5 and 2.x on PHP 8.2/8.3

Compatibility notes

• filter() and map() gained native Collection return types in 3.x; FilesCollection::filter(): self is a valid covariant override ✓
• Internally filter() still uses createFrom() → new static(), so subclasses continue to receive their own type at runtime ✓
• No GrumPHP code extends any of the classes made final in 3.x (Criteria, Expr\*, ExpressionBuilder) ✓

Checklist

• Branch: v2.x
• Bug fix: no
• New feature: no
• BC breaks: no
• Deprecations: no
• Fixed tickets: N/A

[veewee]

Thanks!