Add NoDiscard attributes

[Baptouuuu]

Fix #24

[codecov]

Codecov Report

❌ Patch coverage is 99.83553% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 99.92%. Comparing base (147cd93) to head (f709033).
⚠️ Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/Timezone.php	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             develop      #28   +/-   ##
==========================================
  Coverage      99.92%   99.92%           
  Complexity       751      751           
==========================================
  Files             56       56           
  Lines           2505     2505           
==========================================
  Hits            2503     2503           
  Misses             2        2           

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