Reduce circular dependencies

[Baptouuuu]

Problem

Same as Innmind/framework#3

Solution

Same as Innmind/framework#3 for lazy monads.

For deferred monads we capture a weak reference to $this and the callable that will generate the value. At unwrap time if the weak reference still holds a value then the user still holds a reference to the monad so we call the unwrap method on it so both the initial value is memoized and the mapped value where we unwrap. If it doesn't contain a value it means the monad was freed from memory and so there's no need to store the intermediary value, we can call the callable to generate the value.

[codecov]

Codecov Report

Attention: Patch coverage is 99.39759% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.42%. Comparing base (085455d) to head (a26cc19).
Report is 11 commits behind head on develop.

Files with missing lines	Patch %	Lines
proofs/maybe.php	96.96%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #26      +/-   ##
=============================================
+ Coverage      97.04%   97.42%   +0.37%     
- Complexity       965      974       +9     
=============================================
  Files             63       64       +1     
  Lines           3252     3376     +124     
=============================================
+ Hits            3156     3289     +133     
+ Misses            96       87       -9     

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