compiler: Introduce operator specialization

[EdCaunt]

WIP - the intention is to allow users to build an operator as per usual, then generate single-use "specialised" versions of it with hardcoded values in the generated code to free up registers

[codecov]

Codecov Report

❌ Patch coverage is 23.69478% with 190 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.06%. Comparing base (8ad5ec1) to head (7afa536).

Files with missing lines	Patch %	Lines
tests/test_specialization.py	15.64%	124 Missing ⚠️
devito/ir/iet/visitors.py	23.52%	39 Missing ⚠️
devito/operator/operator.py	37.93%	17 Missing and 1 partial ⚠️
devito/ir/support/guards.py	57.14%	3 Missing ⚠️
devito/ir/equations/equation.py	33.33%	2 Missing ⚠️
devito/symbolics/extended_sympy.py	0.00%	2 Missing ⚠️
devito/types/dimension.py	66.66%	1 Missing ⚠️
tests/test_pickle.py	66.66%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (8ad5ec1) and HEAD (7afa536). Click for more details.

HEAD has 8 uploads less than BASE

Flag	BASE (8ad5ec1)	HEAD (7afa536)
	18	10

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2812       +/-   ##
===========================================
- Coverage   78.96%   45.06%   -33.91%     
===========================================
  Files         248      249        +1     
  Lines       51089    51319      +230     
  Branches     4422     4436       +14     
===========================================
- Hits        40344    23126    -17218     
- Misses       9937    27259    +17322     
- Partials      808      934      +126     

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