Generate subtree inclusion proofs with cmd/proofgen

[phbnf]

Towards #225.

This PR gives the ability to cmd/proofgen.go to generate testdata/subtreeinclusion json files, like it generates other testdata/ files.
I was not aware that this cmd was in this repo, and generated the proofs manually back then.

This is also a good opportunity to fix the description of some of these probes, which was erroneous.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 151 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.40%. Comparing base (2acfad1) to head (0e03927).

Files with missing lines	Patch %	Lines
cmd/proofgen/main.go	0.00%	151 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #238       +/-   ##
===========================================
- Coverage   58.55%   48.40%   -10.15%     
===========================================
  Files           8        8               
  Lines         649      785      +136     
===========================================
  Hits          380      380               
- Misses        261      397      +136     
  Partials        8        8               

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[AlCutter]

math.MaxUint64 might be clearer?

But I'm also not super sure what this is guarding against, this condition is always true unless leafIdx == MaxUint64, but if leafIdx >= MaxUint64-shift then it's going to overflow anyway?
Am I misunderstanding/missing something?

[phbnf]

Done, with tighter checks. This is because some of the test use boundaries values, and we don't want to shift these.