Discourage the use of approximation with GrisetteSMTConfig

[lsrcz]

Using approx for approximation isn't the preferred way, and we should almost always stick with precise and control the reasoning bit width with the types used during symbolic evaluation.

This pull request discouraged the use of approx, and we no longer require to use precise to indicate that we are doing precise reasoning. It is now the default.

Also, approx is renamed to approximate.

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 50.31%. Comparing base (5f8dd25) to head (ecf02b9).

Files	Patch %	Lines
src/Grisette/Internal/Backend/Solving.hs	40.00%	7 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #218   +/-   ##
=======================================
  Coverage   50.30%   50.31%           
=======================================
  Files         100      100           
  Lines        8452     8455    +3     
  Branches      707      706    -1     
=======================================
+ Hits         4252     4254    +2     
- Misses       3493     3495    +2     
+ Partials      707      706    -1     

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