libcurl-impersonate was not being used properly, as the code was
overriding the headers set by it to prevent detection.
- update the libcurl-impersonate to an actively managed lexiforest
fork
- impersonate Chrome 131
- move the defaultHttpHeaders to http.php, where it belongs
- only set defaultHttpHeaders if curl-impersonate is not detected
- make useragent ini setting optional and disabled by default
- add necessary documentation updates
b7c04f8587