use clock_gettime for time

[bill1600]

Use clock_gettime instead of gettimeofday which is deprecated.

[codecov]

Codecov Report

Attention: Patch coverage is 61.53846% with 5 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@6701a5b). Learn more about missing BASE report.
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
src/libparodus.c	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master      #45   +/-   ##
=========================================
  Coverage          ?   62.20%           
=========================================
  Files             ?        3           
  Lines             ?      643           
  Branches          ?      130           
=========================================
  Hits              ?      400           
  Misses            ?      169           
  Partials          ?       74           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[bill1600]

Also added two tests:

1. a test of re-registrations.
2. a test of sending the SVC_ALIVE message, to be sure that parodus suppresses it.