fix: type fieldUpdatedAt/fieldCreatedAt as Date in CRUD callbacks

[MMMikeM]

Summary

clone() uses a JSON reviver that converts ISO 8601 strings to Date objects at runtime. When fieldUpdatedAt or fieldCreatedAt is specified in syncedCrud, the create/update/delete callback parameters receive Date values for those fields — but the TypeScript types still say string.

This PR makes the types honest by:

• Adding FUpdatedAt/FCreatedAt string literal type params to SyncedCrudPropsBase and all syncedCrud overloads
• Using a CrudCallbackInput utility type that remaps the specified field keys from string to Date
• When neither field is set, types are unchanged (fully backwards compatible)

Before

syncedCrud({
    list: async () => fetchTasks(),
    create: (input) => {
        // TypeScript says input.createdAt is `string`
        // Runtime: input.createdAt is a Date object
        console.log(input.createdAt instanceof Date); // true
    },
    fieldUpdatedAt: 'updatedAt',
    fieldCreatedAt: 'createdAt',
});

After

syncedCrud({
    list: async () => fetchTasks(),
    create: (input) => {
        // TypeScript correctly says input.createdAt is `Date`
        input.createdAt.toISOString(); // ✓ no error
    },
    fieldUpdatedAt: 'updatedAt',
    fieldCreatedAt: 'createdAt',
});

Caveat

TypeScript doesn't support partial type argument inference. If the user explicitly specifies TRemote (e.g. syncedCrud<Task>({...})), FUpdatedAt/FCreatedAt fall back to undefined and the date fields stay typed as string. This only affects the explicit-generic case — the common pattern of letting TRemote be inferred from list/get works correctly.

Test plan

• With both fieldUpdatedAt and fieldCreatedAt set: date fields typed as Date, others unchanged
• Without either field set: all types unchanged (backwards compat)
• With only fieldUpdatedAt: only that field becomes Date, fieldCreatedAt stays string
• Zero new type errors introduced (all 57 existing errors are pre-existing in supabase/tanstack-query/react files)