keep wedged or shared-identity motion searches from locking out users

A stalled VOD read blocked the runner forever, so a wedged job held its user and global slot until restart, and on installs without per-user identity (internal port, or auth disabled without a proxy user header) everyone shared one per-user slot. VOD ffmpeg and ffprobe inputs now use a 30 s rw_timeout, a cancel also drops queued parallel runs, a cancelled job stops counting after 60 s, and the per-user limit only applies when the request carries a real username. A failed runner start also stops its requestor.

frigate/test/test_motion_search_decode.py

@@ -101,6 +101,7 @@ class TestVodDecodeCommand(unittest.TestCase):
         joined = " ".join(cmd)
         self.assertIn("-skip_frame nokey", joined)
         self.assertIn("-protocol_whitelist pipe,file,http,tcp", joined)
+        self.assertLess(cmd.index("-rw_timeout"), cmd.index("-i"))
         self.assertIn(f"-i {self.URL}", joined)
         self.assertIn("crop=100:80:10:20", joined)
         self.assertIn("scale=50:40", joined)