feat: add sample timeout for gscam stream recovery

[KirillHit]

Problem

gscam can hang indefinitely when a stream temporarily stops producing samples, so reopen_on_eof may never get a chance to reopen the pipeline. This was observed with looped RTSP streams that periodically restart.

Cause

gscam waits for frames with gst_app_sink_pull_sample(), which can block indefinitely if the RTSP pipeline stays alive but no new samples arrive. In that state, reopen_on_eof does not get a chance to reopen the stream.

Solution

Add an optional sample_timeout_ms parameter. When set, gscam uses gst_app_sink_try_pull_sample() with that timeout. If no sample is received, the loop exits and the existing reopen_on_eof logic restarts the stream. Default is 0, preserving the previous blocking behavior.