Prepare 0.1 code for the 0.2 upgrade

[delacry]

Bridge release for 0.1.8: everything a 0.1 user needs to make their code work on both 0.1 and 0.2 before bumping the constraint.

onEach(), onEachKey(), onEachValue(). 0.2 makes forEach(), forEachKey() and forEachValue() return void and moves chaining to onEach*(). The onEach*() methods ship here already, so chained calls can switch now:

$users->forEach(fn (User $u) => $u->touch())->filter(...); // breaks on 0.2
$users->onEach(fn (User $u) => $u->touch())->filter(...);  // works on 0.1.8 and 0.2

They are real methods in CollectionLogic and MapLogic, but the interfaces declare them through @method tags rather than natively. Adding a method to an interface would break classes implementing it without the logic traits, which 0.2 may do but a 0.1 patch should not. Each interface narrows the return type the same way its forEach*() does, so PHPStan and IDEs keep the precise type along a chain (ImmutableList::onEach(): ImmutableList<E>, MutableTrackedMap::onEach(): MutableTrackedMap<K,V>&TrackedResult, ...).

forEach*() itself is unchanged and not deprecated: it stays in 0.2, only the return type changes, and PHP cannot tell whether a caller uses the result. After upgrading, PHPStan reports every affected call as Result of method ...::forEach() (void) is used.

mapOfPairs() without arguments. 0.2 makes $data required, matching mutableMapOfPairs(). Calling it with no arguments now triggers E_USER_DEPRECATED pointing to mapOf(); an explicit empty iterable stays silent.

UPGRADE-0.2.md. Lists every break with its replacement: forEach*() returning void, mapOfPairs() requiring its argument, MapLogic declaring $store (with exactly which $store declarations now fail and which do not), and the methods direct interface implementers must add. Also notes the zip() behaviour change and the new NoctudCollectionException marker. It should be cherry-picked onto 0.2.x as well.

The API reference and cheatsheet mention onEach*() and the upcoming forEach*() change.

Tests: onEach*() runtime tests ported from 0.2.x; tests/Type/OnEachTypeTest.php pins the narrowed return type on all 24 interfaces; mapOfPairs() with and without arguments.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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