Run tests with Blackbox

[Baptouuuu]

This PR switch the execution of tests from PHPUnit to BlackBox (to be aligned with other packages).

It adds new proofs to make sure all values objects are always within the bounds declared statically.

Adding a proof to Period showed that the behaviours wasn't always consistent. The declared bounds have been modified to make sure it always contains consistent data no matter the way periods are used.

It also showed that PointInTime\Year::numberOfDays() declared type wasn't correct.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (ba1e043) to head (b0665e1).
Report is 10 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop       #6      +/-   ##
=============================================
+ Coverage      99.88%   99.90%   +0.01%     
- Complexity       686      687       +1     
=============================================
  Files             51       59       +8     
  Lines           1726     2073     +347     
=============================================
+ Hits            1724     2071     +347     
  Misses             2        2              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests