Do ReplaceWith

[HoshinoTented]

Replace deprecated first/last/firstOption with getFirst/getLast/findFirst.

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (1206ac9) 81.79% compared to head (e0f5cc2) 81.79%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
...c/main/java/org/aya/tyck/unify/TermComparator.java	66.66%	1 Missing and 1 partial ⚠️
.../src/main/java/org/aya/tyck/unify/Synthesizer.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1017   +/-   ##
=========================================
  Coverage     81.79%   81.79%           
  Complexity     3471     3471           
=========================================
  Files           287      287           
  Lines         10640    10640           
  Branches       1281     1281           
=========================================
  Hits           8703     8703           
  Misses         1216     1216           
  Partials        721      721           

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