Filterx parse leef 2.0

[bshifter]

This PR adds support for the LEEF 2.0 format, specifically focusing on its dynamic header field, delimiter. The task required a significant refactor of the event-parser base module and the unit test framework. Additionally, it introduces optional named arguments for the filterx function, allowing for forced overrides of pair-separator and value-separator. This enhancement will enable us to parse specific non-standard CEF/LEEF messages more effectively.

examples:

filterx {
  dict = {};
  dict.A = parse_cef($MSG, pair_separator="^", value_separator="#");
  dict.B = parse_cef($MSG);
  dict.C = parse_leef($MSG);
  dict.D = parse_leef($MSG, pair_separator="|");
}