feat: add un/serialize for currency

[Chris53897]

We use https://github.com/doctrine-extensions/DoctrineExtensions for Versioning.
I came across the problem, that versioning does not work for Curreny.
Symfony via https://github.com/TheBigBrainsCompany/TbbcMoneyBundle

We use this Attribut.

#[ORM\Column(options: ['default' => 'EUR'])]
#[Gedmo\Versioned]
public $currency = null;

public function setCurrency(Currency $currency): self
    {
        $this->currency = $currency;
        return $this;
    }

    public function getCurrency(): Currency
    {
        return new Currency($this->currency);
    }

This PR solves the problem for us.
But i am not sure if we use it, how it should be used.
Sideeffekts of this PR?

[frederikbosch]

We will not implement. We have parsers and formatters. Regarding ORM mapping: this should be fixed inside the ORM layer.