Asv benchmarks for cellfinder workflow

[sfmig]

This PR adds asv benchmarks to time the workflow defined in #15

The benchmarks time the full workflow and also its individual steps. They are grouped under classes: the time_ methods of one class share setup and teardown functions and other benchmark attributes.

Some points where feedback is welcome:

• I am not sure we really need a teardown function after each benchmark.... 🤔 (right now it just removes the cellfinder-benchmark temporary directory)

• I was looking for a way of defining setup functions for each benchmark abstracting the common bits to avoid too much repetition. I ended up with this approach that uses the @classmethod decorator, but not sure it is the best way (I'm not super familiar with OOP). I also considered setup_cache but I think it serves a different purpose (mainly running computationally intense setup methods only once). I basically wanted to do what it says in the docs:

  You can also include a module-level setup function, which will be run for every benchmark within the module, prior to any setup assigned specifically to each function",

  but not sure how. Any thoughts welcome!

• Should we have the benchmarks in a different repo? I know we want to minimise number so maybe here they are fine. I don't see strong arguments for or against apart from that one.

• Is it repetitive to benchmark the whole workflow and also its parts? Should we just benchmark the whole, and rely on profiling when issues are found?

• the main advantage of asv seems its ability to identify performance regressions across commits....but here the commits we track against would be those from the workflows repo. I understand it would be more interesting for us to track performance regressions for the cellfinder-core commits right? I think it could be done but we may need to rethink the structure.

---

replace "cellfinder-core" with "cellfinder"

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (8665e74) 0.00% compared to head (c100671) 0.00%.
Report is 3 commits behind head on main.

Additional details and impacted files

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Files Changed	Coverage Δ
brainglobe_workflows/__init__.py	0.00% <0.00%> (ø)
brainglobe_workflows/cellfinder/cellfinder_main.py	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[sfmig]

superseded by #94