Fix ModelRunList styles and pagination

[floryst]

• The pagination wasn't working properly, as limit was being sent rather than page and the server is using PageNumberPagination. This meant that triggering pagination would result in the same model run list being sent for each request.
• The styles for the model run list caused it to slightly overflow the bottom of the sidebar, resulting in some cut-off. This becomes more evident if elements are added to the top of the sidebar. Flexbox + overflow handling fixes this issue.

These are issues I discovered as I was moving the loadModelRuns function out of the ModelRunList component and into the store. I'll be looking to add cleaner pagination handling when I do so.

[floryst]

The failing test (test_list_model_run_rest_list) is failing because we are now returning a page size of 10 instead of the default 100. Do we want GET /model-runs/ to return a page size of 10 or 100 (or another value)? I kept with 10 because that's what the ModelRunList.vue component wanted with const limit = 10.

The easiest solution is to only bulk create 10 items in the test rather than 20.