Use Period instead of ElapsedPeriod to express timeouts

[Baptouuuu]

This helps reduce the number of conversions and the potential errors associated with it.

[codecov]

Codecov Report

❌ Patch coverage is 95.45455% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.97%. Comparing base (7524837) to head (b3f3a4b).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/Transport/Connection/Heartbeat.php	66.66%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #16      +/-   ##
=============================================
- Coverage      95.97%   95.97%   -0.01%     
  Complexity      1380     1380              
=============================================
  Files            210      210              
  Lines           9477     9471       -6     
=============================================
- Hits            9096     9090       -6     
  Misses           381      381              

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