fix/ci: add fuzz and flamegraph jobs for PRs

[drahnr]

Goals of this PR are that from now on each and every PR

• [x] is fuzzed with n iterations of fuzzing to assure no new errors are introduced
• [x] comments with a flamegraph of the test run
• [ ] automatically exhibits performance changes compared to master

(also acts as a initial bug squeching guinnea pig so most tooling edge cases are resolved before tackling smth bigger)

[sirmergealot]

🔥 flamegraph 🔥