VFB-291 Install Jest and write a unit test

What's changed

Tested getClientParcelsData.ts using Jest.

[x] The ticket is up-to-date - Please document any deviations from the original approach if there is any.
[x] I have documented the testing steps for QA
[x] I have self-reviewed this PR
[x] Make sure you've verified it works via npm run dev
[x] Make sure you've verified it works via npm run build and npm run start
[x] Make sure you've fixed all linting problems with npm run lint_fix
[x] Make sure you've tested via npm run test

If you have made any changes to the database...

[x] The migration files are up-to-date with my final set up (npx supabase db diff -f <name_of_migration> should create nothing at this point)
[x] I have updated the typescript definitions for the database with npm run generate_types:local
[x] I have modified the seed in supabase/seed/seed.mts if appropriate
[x] If I have modified the seed, I have also generated the seed with npm run db:generate_seed
[x] With my final set up, I can run npm run reset_supabase without any errors.
[x] (Just before merging the ticket) I have updated the timestamps of the new migration files so that they are after all existing migration files.
[x] If I have added constraints e.g. set not null, I have taken reasonable measures to ensure constraint violations do not happen when the migration occurs.
[x] I have checked that migration can happen successfully without resetting the database, doing the following.
- Make sure you have rebased your branch onto dev or merged dev into your branch.
- Checkout the dev branch
- Run npm run post_checkout to reset the database, including the seed data.
- Checkout your branch
- Run npx supabase migrations up --include-all --local to run all outstanding migration files
- Check that the resulting database is what you expect, bar any seed data changes.