Add Closure support to items() for lazy evaluation

[WarLikeLaux]

Q	A
Is bugfix?	❌
New feature?	✔️
Docs added?	❌
Tests added?	✔️
Breaks BC?	❌

What does this PR do?

Adds Closure support to items() in Breadcrumbs, Dropdown, and Menu for lazy evaluation.

When a widget is configured via DI container, items are defined before runtime data (repositories, current user, locale) is available. Passing a Closure defers item resolution until render() is called.

Menu::widget()
    ->items(fn() => $this->buildMenuItems())
    ->render();

Array input works exactly as before.

No BC break: the items() parameter type is widened from array to array|Closure, so all existing calls remain valid.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (011785f) to head (113a785).

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #148   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       289       292    +3     
===========================================
  Files              8         8           
  Lines            911       914    +3     
===========================================
+ Hits             911       914    +3     

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[samdark]

Should be documented with an example on why/when it's needed.

[WarLikeLaux]

Should be documented with an example on why/when it's needed.

Added docs and fixed the changelog number.

While writing the documentation I realized the main use case I had in mind (DI widget definitions) doesn't actually work well in practice. With Yii3's ArrayDefinition, method arguments are passed as plain values, so the Closure inside a DI config has no access to the container or runtime services. The only scenario left is when a widget instance is created early and rendered later, but in most cases you can just pass the array directly at render time.

If you think this feature doesn't carry its weight, I'm fine with closing the PR.