fix(signals): preserve entity when id changes number to equivalent string

[adxdits]

PR Checklist

#5218

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

In updateEntitiesMutably (used by updateEntity, updateEntities, and updateAllEntities), when an entity's ID is changed to a value that is a different type but the same object key (e.g. numeric 1 to string '1'), the entity is deleted instead of updated. This happens because the new key is written before the old key is deleted, and JavaScript treats 1 and '1' as the same object property, so the delete step removes the just-written entity.

Reproduction:

const Store = signalStore({ protectedState: false }, withEntities<Entity>());
const store = new Store();

patchState(store, addEntity({ id: 1, name: 'Ada' }));
patchState(store, updateEntity({ id: 1, changes: { id: '1' } }));

store.entityMap(); // {} entity is lost
store.entities();  // [undefined]

What is the new behavior?

The old entity key is deleted before the updated entity is assigned to the new key, so entities are preserved when the ID's string/number representation changes. entityMap, ids, and entities all stay consistent.

A regression test was added in update-entity.spec.ts covering the numeric-to-string ID update case.

Does this PR introduce a breaking change?

No

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[timdeschryver]

Thanks @adxdits