Change fuzzbench_qemu fuzzer

[tokatoka]

• don't test libpng
• instead run the same harness as fuzzbench to see if it find objectives or not
• added these too to self-hosted ci

but it doesn't work as I said in discord.
this is probably due to signal handling is broken in Qemu?

also fuzzbench_fork_qemu doesn't seem to detect any new edges. can you check that too when you are back? @rmalmain

[tokatoka]

I forgot to say this.
but fuzzbench_fork_qemm doesn't seem to be correctly instrumented @rmalmain

[rmalmain]

yes i realized with the ci, i am still debugging this one.
fuzzbench_qemu test works correctly locally at least now.

[rmalmain]

i fixed fork executor and reduced some trait bounds as well.
should be good to go, works locally

[tokatoka]

ok ok Rust toolchanins are broken as always!! 👎 😠

[tokatoka]

qemu fuzzer still reporting errors

[rmalmain]

yes it's normal, i also fixed the fork executor harness' signature

[tokatoka]

depends on #2496