fix: align %p behavior with native C Lua

[paq]

In C Lua, when checking if a character matches %p, it uses C's ispunct function. Unlike C#'s char.IsPunctuation, ispunctalso matches characters like =. For example, in C Lua, the following expression evaluates to true:

string.gsub("abc=xyz", "(%w*)(%p)(%w+)", "%3%2%1-%0") == "xyz=abc-abc=xyz"

This PR aligns the behavior of %p with that of C Lua as described above.