Make branching timeouts more advanced

[igorganich]

Is your feature request related to a problem? Please describe.
When checking some complex setup, it is common case when some paths are not covered well because of branching solvers timeouts, especially on working machines with weak CPU. Halmos doesn't print any messages about branching solver timeouts and it may be not obvious for a user that something is wrong and solver-timeout-branching parameter should be increased.

Describe the solution you'd like
I see several ways to enhance it:

1. Print timeout rate during execution (just like op/s rate, print successful/timeouted branching statements) so user can see that rate is high and increase it in the next run. Or print Halmos warning when it see that timeout rate is high.
2. Make dynamic solver-timeout-branching option, that is derived from op/s rate. For example, in the start of run 1 ms may be enough, but the longer the run lasts, the more difficult calculations become and op/s rate becoming lower. It is pretty natural for me that branching timeout should be increased in such case.