Log exception in scan and command methods

[shihab-dls]

Fixes #146

This PR adds a callback to scan coroutines that raises their exception if they fail. SoftIOC command exceptions were already being displayed on terminal, whereas p4p command exceptions were not; these tracebacks are now printed to terminal.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.24%. Comparing base (c3f8d50) to head (6f61ae2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
+ Coverage   92.22%   92.24%   +0.02%     
==========================================
  Files          40       40              
  Lines        2070     2077       +7     
==========================================
+ Hits         1909     1916       +7     
  Misses        161      161              

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[shihab-dls]

Returning to this PR, it seems that the current state is that command's that raise exceptions are printed to the terminal. So, we can remove the specific print statement I added in pva. Scan routines that raise exceptions are not printed without the changes introduced in this PR, so that should stay.

[shihab-dls]

I've brought the branch back up to date, so I'm re-requesting a review. I could not reproduce having a command raise an exception and not seeing it on the terminal, so I've focused this PR on scan