feat: Add skribe-fuzz binary for LibAFL fuzzer to the nix derivation

[gtrepta]

• Splits off a skribe-kdist derivation that both skribe-fuzz and skribe depend on
• Adds a skribe-fuzz derivation for the fuzzer binary

[juliankuners]

Please add integration or smoke tests for the skribe-fuzz part using the nix derivation. It could be that the binary builds properly, but fails at runtime for a variety of reasons.

E.g., you can run integration tests like in stable-mir-json, see https://github.com/runtimeverification/stable-mir-json/blob/885ab4a9f6dd1b5416b57e914082fbb341c89f97/.github/workflows/test.yml#L212 and https://github.com/runtimeverification/stable-mir-json/blob/885ab4a9f6dd1b5416b57e914082fbb341c89f97/nix/test/integration.nix .

.github/workflows/test.yaml:120 already, e.g., runs a smoke test of skribe using the nix build on both Linux and MacOS.

Other than this and the single comment, this looks really good to me.

[juliankuners]

Also add the .gitignore in the skribe-fuzz-rs directory. This will also allow you to leave out target here.

Suggested change

	lib.cleanSource (nix-gitignore.gitignoreSourcePure [
	../../.gitignore
	"result*"
	"target/"
	] ../../skribe-fuzz-rs
	)
	lib.cleanSource (nix-gitignore.gitignoreSourcePure [
	../../.gitignore
	../../skribe-fuzz-rs/.gitignore
	"result*"
	] ../../skribe-fuzz-rs
	)

[juliankuners]

Btw, is skribe-fuzz also meant to be run standalone without skribe? Because if that is the case, we would probably want to add the skribe-fuzz binary in skribe.