Random refactoring, preparing for fixing Prop tycking

[ice1000]

These commits have been in my disk for so long so I have made up my mind to create a PR for them

[codecov]

Codecov Report

Merging #880 (8c64be2) into main (16daf93) will increase coverage by 0.07%.
The diff coverage is 52.94%.

@@             Coverage Diff              @@
##               main     #880      +/-   ##
============================================
+ Coverage     82.17%   82.24%   +0.07%     
- Complexity     3386     3388       +2     
============================================
  Files           288      288              
  Lines         10536    10528       -8     
  Branches       1258     1254       -4     
============================================
+ Hits           8658     8659       +1     
+ Misses         1166     1163       -3     
+ Partials        712      706       -6     

Impacted Files	Coverage Δ
base/src/main/java/org/aya/core/term/PiTerm.java	70.17% <ø> (-1.76%)	⬇️
...ase/src/main/java/org/aya/core/term/SigmaTerm.java	84.78% <ø> (ø)
...src/main/java/org/aya/cli/parse/AyaGKProducer.java	89.83% <ø> (ø)
.../src/main/java/org/aya/tyck/tycker/PropTycker.java	64.28% <28.57%> (+17.22%)	⬆️
base/src/main/java/org/aya/tyck/ExprTycker.java	90.52% <57.14%> (+0.96%)	⬆️
base/src/main/java/org/aya/tyck/StmtTycker.java	90.27% <100.00%> (ø)
.../src/main/java/org/aya/tyck/unify/Synthesizer.java	61.53% <100.00%> (+1.92%)	⬆️

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[ice1000]

bors r+

[bors]

Build succeeded:

• commit-check
• gradle-check

[ice1000]

In fact the entire PR is just for this line ;)