~ and @ in the cmdline processor must only be used as suffixes

[theseion]

As discussed in coreruleset/coreruleset#3917, crs-toolchain currently assumes correct placement of ~ and @, i.e., at the end of a regular expression as the last token of the line. This is not enforced, however, so

1. it is impossible to write a regular expression that contains ~ or @
2. ~ and @ are replaced at all positions of a line, causing errors because the replacement expressions are not designed for use anywhere else than as a suffix
3. ~ and @ cannot be escaped