vapoursynth: Improve lsmas plugin version detection

Some lsmas versions (like HomeOfAviSynthPlusEvolution's, the currently
actively maintained one) support the "cachedir" argument but do not
have a "Version" function. Hence, it's better to just check for the
argument directly.

automation/vapoursynth/aegisub_vs.py

@@ -195,7 +195,8 @@ def wrap_lwlibavsource(filename: str, cachedir: str | None = None, **kwargs: Any
 
     ensure_plugin("lsmas", "libvslsmashsource", "To use Aegisub's LWLibavSource wrapper, the `lsmas` plugin for VapourSynth must be installed")
 
-    if b"-Dcachedir" not in core.lsmas.Version()["config"]: # type: ignore
+    import inspect
+    if "cachedir" not in inspect.getfullargspec(vs.core.lsmas.LWLibavSource).args:
         raise vs.Error("To use Aegisub's LWLibavSource wrapper, the `lsmas` plugin must support the `cachedir` option for LWLibavSource.")
 
     clip = core.lsmas.LWLibavSource(source=filename, cachefile=cachefile, **kwargs)