Case-insensitive Unicode manipulation

[ashvardanian]

Python strings offer a lot of powerful methods, such as:

• isalnum, isalpha, isascii, isdecimal, isdigit, isspace, islower, isupper, istitle, isnumeric for checks.
• lower and upper that copy the string.
• casfold described in section 3.13 of the Unicode Standard.

There are very few C-level libraries that provide such functionality, and most of them are not characterized by speed. Covering a subset of that functionality in StringZilla makes sense.

[ashvardanian]

Starting with v3, part of this functionality is already available for ASCII strings. Implementing the same for UTF8 would involve preparing huge dictionaries, and potentially designing some SIMD-friendly trie or automata. So we are not rushing those features for now.