* One use statement
* Add stdin uri scheme
* Convert parse_signer_source to return Result
* A-Z deps
* Convert Usb data to Locator
* Pull DerivationPath out of Locator
* Wrap SignerSource to share derivation_path
* Review comments
* Check Filepath existence, readability in parse_signer_source
* Replace custom DerivationPath impl
* Add method to parse full-path from str with hardening
* Convert Bip44 to trait
* Hoist more work on derivation-path
* Privatize Bip44 trait