[12.x] Add callback to customize fresh timestamp creation for all models

[AndrewMast]

This is an alternative to PR #58614.

Why

Like @aimeos pointed out in the PR, sometimes the implementation for creating fresh timestamps needs to be changed. While this can be accomplished by overriding the freshTimestamp method for a specific model, you might need to change the behavior for all models, in the case with storing timestamp values into a SQL Server database.

This PR adds a Model::freshTimestampsUsing($callback); method to accomplish this. It also adds a Model::freshTimestampsWithoutMicroseconds(); method to simply change the fresh timestamp logic to Date::now()->startOfSecond(), like @aimeos originally had in their PR.

What

Added the following to HasTimestamps trait to allow for a custom fresh timestamps callback:

/**
 * The callback that should be used to create fresh timestamps.
 *
 * @var (\Closure(): \Illuminate\Support\Carbon)|null
 */
public static $freshTimestampsCallback;


/**
 * Set a callback that should be used to create fresh timestamps.
 *
 * @param  \Closure(): \Illuminate\Support\Carbon  $callback
 * @return void
 */
public static function freshTimestampsUsing($callback)
{
    static::$freshTimestampsCallback = $callback;
}

/**
 * Create fresh timestamps without microseconds.
 *
 * @return void
 */
public static function freshTimestampsWithoutMicroseconds()
{
    static::$freshTimestampsCallback = fn () => Date::now()->startOfSecond();
}

And updated freshTimestamp to use the callback:

/**
 * Get a fresh timestamp for the model.
 *
 * @return \Illuminate\Support\Carbon
 */
public function freshTimestamp()
{
    if (static::$freshTimestampsCallback) {
        return call_user_func(static::$freshTimestampsCallback);
    }

    return Date::now();
}

Tests

Still working on tests, would appreciate tips as I don't write tests often.

[taylorotwell]

Merged other PR.

[aimeos]

@AndrewMast Thanks but I only wanted to get a consistent default behavior across all supported databases. Nevertheless, the changing the timestamp format across all models can be useful if someone needs high resolution timestamps with microseconds. Only the freshTimestampsWithoutMicroseconds() method isn't necessary.