paginate over compare runs endpoint

[austin3dickey]

Corresponding to conbench/conbench#1527.

[austin3dickey]

Got this locally (probably will see it once the build completes too):

❯ checking for portable file names ... NOTE
  Found the following non-portable file path:
    conbenchcoms/tests/testthat/resp-class/localhost/api/compare/benchmark-results/10aded...0af-81f373.json
  
  Tarballs are only required to store paths of up to 100 bytes and cannot
  store those of more than 256 bytes, with restrictions including to 100
  bytes for the final component.
  See section ‘Package structure’ in the ‘Writing R Extensions’ manual.

Any suggestions for reconciling this with how the mocking package works?

[boshek]

Thanks for this!