chacha20: remove deprecated math.max_u32 in favour of builtin max_u32

[blackshirt]

This small pull request fixs some spurious warning within x.crypto.chacha20 something related to deprecated constant from math.max_u32 with warning message :
warning: const `math.max_u32` has been deprecated since 2023-12-31, it will be an error after 2024-06-28; use built-in constant `max_u32` instead

Besides changing to the builtin max_u32, this pull request also includes some bits of cleaning and restructuring:

• removes some bits of test data and move into core chacha_test.v file, and deletes test_data from repo.
• removes unnecessary bits from common.v something related to poly1305 one-time key generation, its already built into this module.
• moves some helper and core functions from common.v to the core chacha.v and delete common.v from repo.

Thanks

[spytheman]

Excellent work.

[blackshirt]

Excellent work.

Thank you

[joe-conigliaro]

Thanks @blackshirt

[blackshirt]

Thanks @blackshirt

You're welcome