x.crypto.chacha20poly1305: move up responsibility for allocs into higher caller

[blackshirt]

This patch was related with previous merged PR in #25569. This PR fundamentally does not changes the core functionality. The reason for this changes was to move up buffer allocation in psiv_encrypt_internal and psiv_gen_tag into the caller responsible to do that allocs, especially in .encrypt and .decrypt. It also acts as preliminary step to move into fixed arrays.

This patch contains changes in the means of :

• The main one was a changed in the signature of psiv_encrypt_internal and psiv_gen_tag to accept output buffer as the first params and adapts in another places that call both of them.
• Updates comments on the code
• Removes out left unused remaining bits, ie split_tag helper
• Adjust the tests

Thanks,
Cheers

[tankf33der]

All passed. OK.

[blackshirt]

All passed. OK.

Thank you

[spytheman]

Excellent work.
Thank you @blackshirt 🙇🏻 .