make adler32 available to users

[massimosala]

It is already implemented here:

https://github.com/micropython/micropython/blob/master/lib/uzlib/adler32.c

Can you please make this a public method, in uzlib or hashlib?

It's a good implementation, rewriting it in Python is a waste of time and you have a slow routine.
IMHO adler32 is still useful in many cases, where other checksums are too expensive.

[massimosala]

See the PR

#15322