Hotfix/use steady_clock to handle backward system clock adjustments

[PengZheng]

Monotonic clock should be used to handle backward system clock adjustments correctly.
This PR is a tiny "last boy scout rule" cleanup.

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (8956987) 83.47% compared to head (3e1a6b9) 84.25%.
Report is 9 commits behind head on master.

❗ Current head 3e1a6b9 differs from pull request most recent head 6e364bb. Consider uploading reports for the commit 6e364bb to get more accurate results

Files	Patch %	Lines
...te_service_admin_dfi/src/import_registration_dfi.c	0.00%	1 Missing ⚠️
libs/framework/include/celix/BundleActivator.h	50.00%	1 Missing ⚠️
...ramework/include/celix/dm/ServiceDependency_Impl.h	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #698      +/-   ##
==========================================
+ Coverage   83.47%   84.25%   +0.77%     
==========================================
  Files         254      248       -6     
  Lines       32988    31124    -1864     
==========================================
- Hits        27538    26223    -1315     
+ Misses       5450     4901     -549     

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