[task][maybe] add optional limit parameter to getsz/putsz

[Alexander Belchenko]

That's inspired by the idea about how to on serial number (as const char[]).
It would be nice to add optional limit parameter to getsz/putsz api, so users of such api can prevent themselves to shoot in the leg.

E.g.

def getsz(self, addr, limit=None):

if limit is not None and > 0 - read max of (limit-1) characters not including trailing zero. But expect it there. Maybe raise error if trailing zero not found within (limit) bytes.

def putsz(self, addr, s, limit=None):

if limit is not None and > 0 - write string only if it fits into limit bytes, including terminated zero character.