Simplify headers

[Baptouuuu]

This boils down to making all classes final and removing interfaces.

Many Header\*Value have been removed to force the constraints on the associated header constructor. The ones not being deleted have been moved to more appropriate namespaces.

[codecov]

Codecov Report

Attention: Patch coverage is 95.41096% with 67 lines in your changes missing coverage. Please review.

Project coverage is 96.17%. Comparing base (457ce2a) to head (2ce7c39).
Report is 52 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/ResponseSender.php	0.00%	31 Missing ⚠️
src/Header/ContentRange.php	75.00%	8 Missing ⚠️
src/Header/Range.php	77.77%	6 Missing ⚠️
src/Header/SetCookie.php	86.11%	5 Missing ⚠️
src/Header/Host.php	80.00%	2 Missing ⚠️
src/Header/SetCookie/Domain.php	75.00%	2 Missing ⚠️
src/Header/SetCookie/Expires.php	81.81%	2 Missing ⚠️
src/Header/SetCookie/Path.php	75.00%	2 Missing ⚠️
src/Header/Age.php	88.88%	1 Missing ⚠️
src/Header/ContentLength.php	91.66%	1 Missing ⚠️
... and 7 more

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #16      +/-   ##
=============================================
+ Coverage      95.51%   96.17%   +0.66%     
+ Complexity      1245     1094     -151     
=============================================
  Files            235      197      -38     
  Lines           5039     4709     -330     
=============================================
- Hits            4813     4529     -284     
+ Misses           226      180      -46     

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