feat: add basic support for otpauth:// URI parsing

This change provides a bare minimum implementation to parse an otpauth:// type URI into its component parts.
Parsing is quite lax, and focused on what Keysmith can support or recover from in the intended UI/UX for adding accounts via QR codes.

See-Also: https://github.com/google/google-authenticator/wiki/Key-Uri-Format
Issues: #14