Function load_plugins_from_dir 

pub fn load_plugins_from_dir(
    dir: &Path,
    builder: &mut PluginRegistryBuilder,
) -> Vec<PluginLoadResult>

Load all plugin shared libraries from dir and register them with builder.

Scans dir for files with the platform-appropriate extension (.so, .dylib, .dll). Each library is loaded, its API version is checked, and its registration function is called.

Returns one PluginLoadResult per library file found.