PR #125 test build: obs-gstreamer.dll (Windows, delay-load fix for #124)

Test build for PR #125, fixing fzwoch#124 (plugin failing to load / empty element registry on OBS 32.2+).

Built from commit 4044627, which also addresses the review feedback on the DLL search path handling:

• Dropped the plugin's own SetDefaultDllDirectories() call - OBS 32.2 already makes it, so the plugin doesn't need to redecide that process-wide policy.
• The AddDllDirectory() cookie is now saved and released via RemoveDllDirectory() in obs_module_unload(), instead of leaking it for the process lifetime.

Install: drop windows/obs-gstreamer.dll from the zip into
%ProgramData%\obs-studio\plugins\obs-gstreamer\bin\64bit\obs-gstreamer.dll
(only the plugin DLL needs to be there - no need to copy any GStreamer runtime files alongside it, and no PATH changes needed). You still need the official GStreamer MinGW runtime installed.

Not an official release - this is a pre-merge test build for anyone following fzwoch#124 / PR fzwoch#125 who wants to try the fix early.