Batch audit data entry improvements

[arsalansufi]

A catch-all issue to document odds and ends that I'd eventually like to get to but couldn't in https://github.com/votingworks/arlo/pull/1661

• [ ] Improve experience when number of batches or number of choices is large, e.g. via sticky elements like a sticky search bar and a sticky tab bar
• [ ] Consider alternatives to rudimentary horizontal scrolling when number of sheets is large, e.g. horizontal scrolling of just the tab bar
• [ ] Improve keyboard navigation, specifically, make popover buttons (e.g. remove sheet) tab accessible and add up-down-arrow navigation to the batch list
• [ ] Add additional tests to cover more nuanced UI interactions
• [ ] Consider moving the "Edit tallies" button to the top right such that it isn't below the fold when there are many contests/choices (https://github.com/votingworks/arlo/pull/1878#discussion_r1488517833)

[arsalansufi]

Display who last updated a batch (JM or tally entry users) is documented in its own issue: https://github.com/votingworks/arlo/issues/1662