Feature/769 libuv package and thread header

[pnoltes]

This PR adds the libuv dependency and creates initial celix_uv_cleanup.h and tests.

Follow up PRs will replace celix_threads.h usage with libuv variants.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.53%. Comparing base (6eca661) to head (9f46175).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #815      +/-   ##
==========================================
+ Coverage   91.43%   91.53%   +0.10%     
==========================================
  Files         234      235       +1     
  Lines       28655    28687      +32     
==========================================
+ Hits        26200    26260      +60     
+ Misses       2455     2427      -28     

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