fix: Swapcase must handle multibyte expansions by joshuamegnauth54 · Pull Request #7559 · RustPython/RustPython

`swapcase` used `to_ascii_lowercase` and uppercase to swap cases. This
is fine for ASCII, but code points may expand into multiple bytes which
leads to incorrect case swaps for some languages. The fix is to use
`to_lowercase` and `to_uppercase` instead.

Unfortunately, this leads to a realloc in `swapcase` when bytes are
expanded.

Part of RustPython#7526.