flake8 giving warnings in recirq/kpz and possibly other subdirectories

[mhucka]

Describe the issue

While testing something, I noticed flake8 is giving warnings for code in recirq/kpz, such as

recirq/kpz/experiment.py:170:61: W605 invalid escape sequence '\m'
recirq/kpz/experiment.py:170:67: W605 invalid escape sequence '\i'
recirq/kpz/experiment.py:180:61: W605 invalid escape sequence '\m'
recirq/kpz/experiment.py:180:67: W605 invalid escape sequence '\i'
recirq/kpz/experiment.py:192:61: W605 invalid escape sequence '\m'
recirq/kpz/experiment.py:192:67: W605 invalid escape sequence '\i'
recirq/kpz/experiment.py:202:61: W605 invalid escape sequence '\m'
recirq/kpz/experiment.py:202:67: W605 invalid escape sequence '\i'
recirq/kpz/experiment.py:237:59: W605 invalid escape sequence '\m'

Running it globally reports a lot more. Perhaps the code base has not been run through flake8 for some time.

How can the issue be reproduced?

One of the CI checks in .github/workflows/ci.yaml runs this command:

flake8 recirq --count --exit-zero --max-complexity=10 --max-line-length=127

This produces many warnings. The CI workflow does not fail despite these warnings because it's passing the --exit-zero flag to flake8.

[mhucka]

The following PRs address some of the warnings:

• PR Use raw strings for docstrings containing LaTeX #429: invalid escape sequences in docstrings
• PR Fix type comparisons to use isinstance #430: use isinstance for type comparisons*
• PR Fix a subset of whitespace consistency issues #431: fix a subset of whitespace consistency issues
• PR Fix #433: remove unused imports #432: remove unused imports