Performance profiling improvements

[dancoates]

• Allow outputting html, json, or text reports
• Json reports can be viewed in https://www.speedscope.app/ for detailed flame charts
• Write file based profiles to a profile folder with a timestamp filename, so that they can be kept over time
• Add documentation about how to enable profiling
• ~Disable file watching unless running locally~

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.36%. Comparing base (9853c70) to head (61606d5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #855 +/- ## ======================================= Coverage 80.36% 80.36% ======================================= Files 169 169 Lines 14336 14337 +1 ======================================= + Hits 11521 11522 +1 Misses 2815 2815 ```

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