This new method can be used for instance in a pipeline during the build
and deployment of the application.
The cache has to be registered first, otherwise the warmup will end up
being useless.
```php
$cache = new \CuyZ\Valinor\Cache\FileSystemCache('path/to/cache-dir');
$mapperBuilder = (new \CuyZ\Valinor\MapperBuilder())->withCache($cache);
// During the build:
$mapperBuilder->warmup(SomeClass::class, SomeOtherClass::class);
// In the application:
$mapper->mapper()->map(SomeClass::class, [/* … */]);
```
Co-authored-by: Romain Canon <romain.hydrocanon@gmail.com>
