The cache implementation that was previously injected in the mapper
builder must now be manually injected. This gives better control on when
the cache should be enabled, especially depending on which environment
the application is running.
The library provides a cache implementation out of the box, which saves
cache entries into the file system.
It is also possible to use any PSR-16 compliant implementation, as long
as it is capable of caching the entries handled by the library.
```php
$cache = new \CuyZ\Valinor\Cache\FileSystemCache('path/to/cache-dir');
(new \CuyZ\Valinor\MapperBuilder())
->withCache($cache)
->mapper()
->map(SomeClass::class, [/* … */]);
```
The `Source` class is a new entry point for sources that are not plain
array or iterable. It allows accessing other features like camel-case
keys or custom paths mapping in a convenient way.
It should be used as follows:
```php
$source = \CuyZ\Valinor\Mapper\Source\Source::json($jsonString)
->camelCaseKeys()
->map([
'towns' => 'cities',
'towns.*.label' => 'name',
]);
$result = (new \CuyZ\Valinor\MapperBuilder())
->mapper()
->map(SomeClass::class, $source);
```
