[10.x] Add ulid testing helpers

[Jasonej]

This PR adds testing helpers to the generation of ULIDs to match what was introduced for UUIDs in #42619.

You can specify a ULID factory.

$ulid = Str::ulid();

Str::createUlidsUsing(fn() => $ulid);

Str::ulid() === $ulid; // true

You can freeze ULID generation which is equivalent to manually specifying a ULID factory as shown above, but doesn't require you to generate and capture a ULID first.

$ulid = Str::freezeUlids();

Str::ulid() === Str::ulid() === $ulid; // true

Str::createUlidsNormally();

When passing a closure it freezes only for the duration of that closure.

Str::freezeUlids(function ($ulid) {
    Str::ulid() === Str::ulid() === $ulid; // true
});

Str::ulid() === Str::ulid(); // false

You can also provide a sequence of ULIDs to return.

Str::createUlidsUsingSequence([
    $zeroth = Str::ulid(),
    $first = Str::ulid(),
]);

Str::ulid() === $zeroth;
Str::ulid() === $first;
Str::ulid(); // back to normally generated ULIDs.

You can skip indexes in a sequence to allow them to be normally generated.

Str::createUlidsUsingSequence([
    0 => ($zeroth = Str::ulid()),
    3 => ($third = Str::ulid()),
]);

Str::ulid() === $zeroth; // true
Str::ulid(); // normally generated
Str::ulid(); // normally generated
Str::ulid() === $third; // true

You can pass a closure to control what happens when there are no more ULIDs in the sequence.

Str::createUlidsUsingSequence([
    $zeroth = Str::ulid(),
    $first = Str::ulid(),
], fn() => throw new Exception('No more ULIDs in sequence'));

Str::ulid() === $zeroth; // true
Str::ulid() === $first; // true
Str::ulid(); // throws

This will impact skipped indexes as well though.

Str::createUlidsUsingSequence([
    0 => ($zeroth = Str::ulid()),
    3 => ($third = Str::ulid()),
], fn() => throw new Exception('No more ULIDs in sequence'));

Str::ulid() === $zeroth; // true
Str::ulid(); // throws