Simplify confluence check

[ice1000]

This PR simplifies confluence check by using a prefix count array data structure for the clause index in MCTs.

It also stores MCTs in the core, which will be helpful later.

[ice1000]

https://www.youtube.com/watch?v=pFjNNz8pyUg&list=PLQnii9h2w777i0GMB8Id86Xy1R62NHLVw&index=13

[codecov]

Codecov Report

Attention: Patch coverage is 97.14286% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.41%. Comparing base (bbf7086) to head (cb5abcb).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
base/src/main/java/org/aya/tyck/StmtTycker.java	94.44%	0 Missing and 1 partial ⚠️
...x/src/main/java/org/aya/prettier/CorePrettier.java	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1285      +/-   ##
============================================
+ Coverage     83.38%   83.41%   +0.02%     
+ Complexity     4239     4235       -4     
============================================
  Files           385      386       +1     
  Lines         12289    12311      +22     
  Branches       1418     1423       +5     
============================================
+ Hits          10247    10269      +22     
  Misses         1291     1291              
  Partials        751      751              

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[ice1000]

Beautiful