Add a lexer for Verifpal

[jvoisin]

Verifpal website: https://verifpal.com/
Verifpal "spec": https://verifpal.com/res/pdf/manual.pdf
Verifpal extension for VSCode: https://source.symbolic.software/verifpal/verifpal-vscode

I'm the author of the testfile, so no licensing issues there :)

[jeanas]

Some minor comments and we should be good to go.

[jeanas]

Also, there are CI failures.

[jvoisin]

I don't understand the linter error:

regexlint: commands[0]> regexlint pygments.lexers
/home/runner/work/pygments/pygments/pygments/lexers/verifpal.py: (VerifpalLexer:queries:pat#2) E108: Nested capture group other than the final one using bygroups
  '(((?:authentication|confidentiality|e...
    ^ here
regexlint: exit 1 (18.85 seconds) /home/runner/work/pygments/pygments> regexlint pygments.lexers pid=1778

[jeanas]

Sorry, that was bad advice from me regarding bygroups() and words(). I forgot that words() introduces a capturing group. So the (words(..., prefix=r'(', suffix=r')( )'), bygroups(X, Y)) translated to (r'((...)( ))', bygroups(X, Y)), which doesn't give the expected result (the first 2 capturing groups are the outer one and the first inner one). I've fixed it.

[jeanas]

Thanks!