test: add real timeout test

[Green-Sky]

I am having troubles with the windows builds making mono_time a random number generator.

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This change is 

[Green-Sky]

On a different setup/repo, I am getting mostly binaries that assert like this:

MonoTimeUnixTimeIncreasesOverTime() succeeded
MonoTimeIsTimeout() succeeded
Assertion failed: !(mono_time_is_timeout(mono_time, start, 5)), file D:\a\tomato\tomato\external\toxcore\mono_time_test.cc, line 76

[Green-Sky]

looks like non of the cmake based compiles run the unit tests, probably because they cant fine gtest.

[Green-Sky]

tomato-windows-msvc-x86_64(51)-good-master-debug-bad-ithink-test-only.zip
If someone could debug this debug binary, would be nice. src

[codecov]

Codecov Report

Attention: 42 lines in your changes are missing coverage. Please review.

Comparison is base (90f7496) 71.55% compared to head (0c998a7) 71.58%.
Report is 2 commits behind head on master.

Files	Patch %	Lines
toxcore/onion_client.c	71.66%	17 Missing ⚠️
toxcore/Messenger.c	0.00%	6 Missing ⚠️
toxcore/onion.c	83.78%	6 Missing ⚠️
toxcore/DHT.c	64.28%	5 Missing ⚠️
toxcore/logger.c	0.00%	2 Missing ⚠️
toxcore/util.c	0.00%	2 Missing ⚠️
toxav/msi.c	0.00%	1 Missing ⚠️
toxcore/network.c	66.66%	1 Missing ⚠️
toxcore/shared_key_cache.c	90.00%	1 Missing ⚠️
toxcore/tox.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2477      +/-   ##
==========================================
+ Coverage   71.55%   71.58%   +0.02%     
==========================================
  Files          75       75              
  Lines       25200    25291      +91     
==========================================
+ Hits        18033    18105      +72     
- Misses       7167     7186      +19     

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