test: add fuzzers for Builder.Export + inclusion.SubtreeWidth

[odeke-em]

In a continuous bid to battle test and secure the network, this change adds 2 fuzzers for:

• Builder.Export
• inclusion.SubtreeWidth

[rootulp]

golangci-lint is failing: https://github.com/celestiaorg/go-square/actions/runs/11416803480/job/31768417818?pr=119#step:5:37

cc: @odeke-em

[odeke-em]

@rootulp thanks for the ping but I think that your repo's helpers are giving y'all bad tips and invalid suggestions

  fuzz_test.go:15: File is not `gofumpt`-ed (gofumpt)
33
  	if err := os.MkdirAll(dirPath, 0755); err != nil {

is idiomatic code and the preferred way for quick throw away values in Go. I am going to change it but I highly suggest in the future taking a look at the suggestions.

[cristaloleg]

is idiomatic code and the preferred way for quick throw away values in Go. I am going to change it but I highly suggest in the future taking a look at the suggestions.

gofumpt reports 0755 which should be 0o755, not the problem you've mentioned.

[odeke-em]

Thank you @cristaloleg! Sadly the CI suggestion did not appear in the error log. Let me update that.

[odeke-em]

For the record, even that suggestion is pedantic per https://go.dev/play/p/CpKnMA6OAKj but let me push up the suggestion still.

[odeke-em]

@cristaloleg we have a panic uncovered in 2 minutes of fuzzing per #120. Kindly please help define what happens so that this change can then be merged. Thank you!

[cristaloleg]

Maybe pedantic but definitely error-prone.

[rootulp]

@odeke-em do you have a concrete suggestion on what linter settings you would like to be changed for this repo? https://golangci-lint.run/usage/linters/#gofumpt doesn't have a setting to disable just this rule:

so we would need to disable gofumpt entirely which doesn't seem desirable. Additionally, that specific lint rule seems like a good suggestion so I propose we keep gofumpt and modify the code to satisfy the linter.