Cannot run fuzzer for a fixed amount of time

[wuestholz]

Describe the bug
I would like to run the hybrid fuzzer for a fixed amount of time (for instance, one hour). It would be great if this was possible (just like for Echidna). Unfortunately, the --test-limit option results in different running times depending on the tested contracts and how much time is spent on executing inputs and solving constraints.

Additional context:

• Operating system: Ubuntu 20.04.5 LTS
• Python version: 3.8.10
• Echidna version: 2.0.4