Add SolveTimer()

[dbrakenhoff]

Short Description

Add a timer for model optimization. I was running into some extremely slow running models somewhere within my 400 model dataset, and found this useful in diagnosing the issue, by printing the model name in my loop and then showing some record of elapsed time and no. of iterations.

It does require tqdm to be installed, so I put it into a different file that is not imported by default. Due to the optional nature of the dependency I haven't added any examples or tests.

Usage:

from pastas.timer import SolveTimer

with SolveTimer() as t:
    ml.solve(callback=t.timer)

This prints the following to the console:

Optimization progress: 73it [00:01, 67.68it/s]

Checklist before PR can be merged:

• closes issue #xxxx
• is documented
• PEP8 compliant code
• tests added / passed
• Example Notebook (for new features)
• API changes documented in Release Notes

[dbrakenhoff]

Oops I committed some stuff in here that should have gone straight to dev. If PR is not accepted, I'll make the changes again on dev.