[Platform] Add support for Cartesia

[Guikingone]

Q	A
Bug fix?	no
New feature?	yes
Docs?	yes
Issues	None
License	MIT

Hi 👋🏻

Here's the PR for the support of Cartesia as a TTS / STT platform.

[Guikingone]

Unpopular opinion to discuss @OskarStark @chr-hertel but IMHO, the CI should not fail if we're using readonly classes.

Small example with the Symfony\AI\Platform\Contract defined as readonly, if I remove the readonly from sub-classes, PHP will throw an error.

Using readonly is not a bad approach IMHO, what's the goal behind this restriction? 🤔

PS: There's little to no chance that one day, we store informations in the *Client classes.

[chr-hertel]

I don't think that this is an unpopular opinion, it's just something that is not easy to have while having to keep up with the BC promise, see symfony/symfony#62168 (comment) for reasoning.