Fixes #2243 These tests rely on some kind of sync between readers and writers, as if circular buffer is overrun, test no longer runs as expected. We use time-sensitive rate limiter to limit write speed to make sure readers can always catch up. Lowering the rate should slow down writers and make tests more likely to succeed. For #2243, the failure was from buffer overrun: when overrun is detected, `Watch` function closes the channel (and test "receives" zero element). Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>