Modernise library & add support for TZ offset and fractional seconds

[jamesacarr]

This PR makes the following changes:

Features

• Add support for timezone offsets via the XXX token
• Add support for fractional seconds via the SSS token

General

• Switch out Travis for GitHub Actions
• Switch out Prettier & ESLint for Biome - native TS support and better performance
• Switch out Ava for Vitest - native TS support and better performance
• Switch out Rollup for Tsup - simpler config
• Add precommit hooks for linting via husky & lint-staged