ext/curl: Deprecate the NTLM_WB constants

[GrahamCampbell]

libcurl removed NTLM_WB support in 8.8.0, so on any current libcurl the CURLAUTH_NTLM_WB bit is silently filtered out of CURLOPT_HTTPAUTH/CURLOPT_PROXYAUTH masks and the CURL_VERSION_NTLM_WB feature bit is never set; only builds against libcurl older than 8.8.0 can still use the feature at all.

This deprecates both constants with #[\Deprecated], following the CURLOPT_BINARYTRANSFER precedent from PHP 8.4, so code still referencing NTLM_WB is nudged to drop it. The NTLMWB key in curl_version()['feature_list'] is kept and continues to report false at runtime. This is also a first step in preparing for curl's scheduled removal of NTLM support altogether in September 2026 (https://curl.se/dev/deprecate.html); the still-functional CURLAUTH_NTLM and CURL_VERSION_NTLM constants are intentionally left alone.