Handle directive-heavy wp-config parsing

[mmaunder]

Summary

• add a targeted WordPress config parser that extracts DB credentials without executing helper directives
• wire the new parser into WordpressSite and tolerate @-prefixed functions when reading wp-config
• cover conditional defines, constant() indirection, host:port parsing, and other wp-config variants with focused unit tests

Testing

• venv/bin/python -m unittest discover -s wordfence -t .

[akenion]

As discussed, I don't think this is the best approach to solve the issue. I'll leave the PR open for now, but am not including this in the upcoming 5.0.2 release.