Relaxed Sized constraints for encoders

[Dekker1]

This allows the more liberal usage of non-sized and dyn objects of
ClauseDatabase. We introduce the AsDynClauseDatabase for placed where
we need to be able to create a dyn ClauseDatabase references. This
trait is automatically implemented for all Sized types and dyn
references, but cannot be automatically implemented for ?Sized types.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 12 lines in your changes missing coverage. Please review.

Project coverage is 72.07%. Comparing base (ff7ecf6) to head (8c00377).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
crates/pindakaas/src/helpers.rs	30.76%	9 Missing ⚠️
crates/pindakaas/src/lib.rs	40.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #80      +/-   ##
===========================================
- Coverage    72.12%   72.07%   -0.06%     
===========================================
  Files           20       20              
  Lines         7355     7377      +22     
  Branches      7355     7377      +22     
===========================================
+ Hits          5305     5317      +12     
- Misses        1923     1933      +10     
  Partials       127      127              

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