options: lower verbosity of option parsing

Since this happens at per-frame level in mpv. Not entirely happy with
this solution but it's better than spamming log. And in practice, we
know what options are being applied anyway, since mpv already logs
`--libplacebo-opts`.

src/options.c

@@ -338,7 +338,7 @@ static bool option_set_raw(pl_options opts, pl_str k, pl_str v)
     return false;
 
 found:
-    PL_DEBUG(p, "Parsing option '%s' = '%.*s'", opt->key, PL_STR_FMT(v));
+    PL_TRACE(p, "Parsing option '%s' = '%.*s'", opt->key, PL_STR_FMT(v));
     if (opt->deprecated)
         PL_WARN(p, "Option '%s' is deprecated", opt->key);