[#73] fix(lib): use jemallocator only on UNIX

[M0dEx]

This PR fixes the following issues:

• Building jemallocator on Windows seems like a hassle with the required dependencies and compilation errors, it will from now on be enabled on UNIX systems only.
• Terminal colours got broken in [#48] fix(utils/tracing): use correct formatting on Windows #63, now they should work again.

The PR also bumps tun2 to version ^2.0.0.

Closes #73.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.35%. Comparing base (a421a18) to head (bb14a9c).

Files	Patch %	Lines
src/utils/tracing.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #74   +/-   ##
=======================================
  Coverage   82.35%   82.35%           
=======================================
  Files          16       16           
  Lines         918      918           
=======================================
  Hits          756      756           
  Misses        162      162           

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