Add F5 TTS pipeline

[ayushtues]

What does this PR do?

Add F5 TTS #10043

[ayushtues]

Okay, got all the code which is needed in two files, and used existing diffusers primitives in some easy to catch places. Now will work on integrating it in the diffusers class structure

[ayushtues]

Attention!

Seems like we can use the diffusers Attention class directly, but need to add a new Processor to support RoPE embeds on selective heads as in F5

[ayushtues]

Tokenization

F5 uses a character level tokenizer for the text, might want to write a simple tokeniser class for it.

Might just be fine to keep it in a simple function for now, since its very straightforward.

[ayushtues]

Tests

Basic structure looks good now, let's add some tests, and then make it more diffusers friendly! Adding tests would also force me to follow the structure more strongly and ensure that the code is not buggy

[ayushtues]

Flow matching/Schedulers

Will also need to use one of the schedulers from Diffusers, I think they use simple Euler method only, but the sway sampling step needs to be accounted for somehow, although its just a change in the discretisation schedule so should be straightforward

[ayushtues]

Future work

• Support streaming (already there in OG F5 repo), although this is more like chunk based inference really. Current model is non-causal so only chunk based streaming makes sense anyway
• Triton server inference, again already there in the F5 repo