Small big step confluence test

[7h3kk1d]

Adds a qcheck test that says if the small steps from the stepper evaluate to a value that should be equivalent to the evaluator. Always chooses the first available step.

It's currently real slow and doesn't find issues every time. I'm also not calling EvaluatorStep.refresh_step which might be important.

Example failure (Fixed in #1657):

FAIL Small step reduction and big step reduction are equal

   Expected: `fun x: (?) -> fun (()): (()) -> x'
   Received: `fun x: (?) -> fun (()): (()) -> x''

`
on `fun x -> fun (()) -> x (after 2 shrink steps)`

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 50.41%. Comparing base (9dc2479) to head (7ac321a).
Report is 7 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1633      +/-   ##
==========================================
+ Coverage   50.08%   50.41%   +0.32%     
==========================================
  Files         130      134       +4     
  Lines       14462    15036     +574     
==========================================
+ Hits         7244     7580     +336     
- Misses       7218     7456     +238     

Files with missing lines	Coverage Δ
src/haz3lcore/dynamics/Evaluator.re	92.98% <ø> (-3.32%)	⬇️
src/haz3lcore/dynamics/stepper/EvaluatorStep.re	60.43% <ø> (ø)

... and 20 files with indirect coverage changes

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