compiler: Patch pickling of GuardFactor and reconstruction

[FabioLuporini]

No description provided.

[codecov]

Codecov Report

Merging #2126 (80dd5d4) into master (d5a4d27) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2126      +/-   ##
==========================================
+ Coverage   87.15%   87.17%   +0.01%     
==========================================
  Files         220      222       +2     
  Lines       39310    39368      +58     
  Branches     5114     5117       +3     
==========================================
+ Hits        34261    34319      +58     
  Misses       4478     4478              
  Partials      571      571              

Impacted Files	Coverage Δ
devito/ir/support/guards.py	56.25% <100.00%> (+0.39%)	⬆️
devito/operator/operator.py	89.17% <100.00%> (+0.02%)	⬆️
devito/passes/clusters/__init__.py	100.00% <100.00%> (ø)
devito/passes/clusters/unevaluate.py	100.00% <100.00%> (ø)
devito/symbolics/unevaluation.py	100.00% <100.00%> (ø)
tests/test_dse.py	99.81% <100.00%> (ø)
tests/test_operator.py	97.73% <100.00%> (ø)
tests/test_pickle.py	99.59% <100.00%> (+0.02%)	⬆️

[mloubout]

nitpickin, maybe FrozenExpr ?