torngit github: set up experiment for list_repos page size

[matt-codecov]

codecov/engineering-team#1757

github docs on timeouts:

If GitHub takes more than 10 seconds to process an API request, GitHub will terminate the request and you will receive a timeout response and a "Server Error" message.
...
For example, if you are requesting 100 items on a page, you can try requesting fewer items.

list_repos() and family use a page size of 100, and we sometimes observe 502s/504s in response after 10 seconds which is github's cutoff. this PR sets up an experiment to test smaller page sizes

this should be running with a user oauth token that has its own rate limit. so this should probably not cause rate limit issues

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.48%. Comparing base (2a8964f) to head (1b2c49a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #232      +/-   ##
==========================================
- Coverage   89.59%   89.48%   -0.11%     
==========================================
  Files         328      324       -4     
  Lines       10481    10367     -114     
  Branches     1915     1900      -15     
==========================================
- Hits         9390     9277     -113     
+ Misses       1024     1020       -4     
- Partials       67       70       +3     

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