ditto : Merge branch 'use-npool-nostrify' into 'main'

Replace PoolStore with NPool & add tests for outbox.ts file and RelayError.ts file

Closes #148, #180, and #181

See merge request soapbox-pub/ditto!424

https://github.com/soapbox-pub/ditto/commit/9cb85e42d25234706101c98c19c5e763c1364b93