feat: fuzz gnovm/pkg/transpiler.Transpile

[odeke-em]

Adds a fuzzer for Transpile, which found bugs:

• gnovm/pkg/transpiler: mangled imports in Gno code cause a panic when generating Go code #3425 in which this following Go program crashed the transpiler

package A
import(""//"
""/***/)

• gnovm: inability to catch unused variables at compile time allows for nuisance programs: deviation from Go #3426 which generated an input that revealed the fact that Gno deviates from Go by allowing unused variables yet Go's standard is strict on unused variables like this program

package main

func main() {
	const c1 = 1 < 8
	main()
	1
}

which we shouldn't allow

• partially gnovm: discrepancy at compile time: no integer overflows reported for Gno program with constants that Go won't compile #3428 which revealed the discrepancy in Gno that the overflow detection is still lacking as the following program is invalid Go but Gno allowed it to run

package main

func main() {
	const c1 = int8(1) << 8
	println(c1)
}

because 1<<8 (256) is higher than the range of int8 for which the maximum is (1<<7) - 1 aka 127

Updates #3087

[Gno2D2]

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[n2p5]

Thanks for doing this. Before we give a LGTM, A couple of things:

• can I get you to clean up that one unused variable in the code that I pointed out?
• Could you add some more context into the PR body explaining what this PR does to give some more context to the issues you've linked it to?

[jefft0]

Removed the review/triage-pending label because this PR was reviewed by core dev n2p5.

[odeke-em]

Gotcha @n2p5, I have added more succinct context to the body/description of the PR per #3457 (comment), please take a look.

[n2p5]

Spoke with @odeke-em on this and we reviewed together.

[thehowl]

@n2p5 Why was this merged with a failing CI?

[n2p5]

ah, @thehowl , that was a mistake, I think I mixed up my tabs here and missed this one.