Summary

adds a new getFileDuration helper function that accepts a URL and attempts to find the duration of the audio/video using JS's Audio class (which, despite its name, works for video too and is a much simpler method to get duration than my originally proposed react-player solution)
- the function will only attempt to fetch the file if it ends in one of the following extensions: ['mp3', 'mp4', 'ogg', 'm4a']. This way, we aren't fetching constantly while the user is typing, and we aren't attempting to fetch stuff that we won't be able to get a duration from. This list can be expanded as needed.
adds functionality to EventForm that watches the file URLs in the form and maintains a mapping of URLs with durations and applies those durations to any matching AV file
- when an AV file's duration has been automatically fetched, its time input is disabled

Video

Name	Link
Latest commit	281a541e28287701d5555086a3e8bada0d597a59
Latest deploy log	https://app.netlify.com/sites/avannotate-staging/deploys/66eb352e88866400087fa0c3
Deploy Preview	https://deploy-preview-111--avannotate-staging.netlify.app
Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.