Share DNS and Connect between curl requests

[staabm]

reduces overhead when doing multiple curl requests per php-request. starting with PHP 8.5 this even allows caching across php-requests.

other places which manually invoke curl_init can benefit in a similar way by adding such code. curl_multi_* will automatically share caches between requests, without the need for additional code.

we could also add CURL_LOCK_DATA_SSL_SESSION, but I was not sure whether this has security implications. therefore I left it out for now.

analog https://github.com/lesstif/php-JiraCloud-RESTAPI/pull/117