As an AntTP user
I want to be able to provide a 3rd party public key and a digital signature
So that I can verify that the owner of the public key has signed the associated data

Given AntTP supports HEAD operations on files within archives to retrieve meta data in response headers
When a HEAD operation is made with the request headers 'x-signature' (populated with a base64 encoded public key)
And 'x-public-key' (populated with a base64 encoded public key)
Then retrieve and base64 decode the value of the 'x-signer-public-key' header as signer_public_key (as bytes) 
And retrieve and base64 decode the value of the 'x-data-signature' header as data_signature (as bytes)
And get_data_archive function in file_controller.rs must be passed signer_public_key and data_signature
And get_archive_binary in archive_service.rs be called to retrieve the bytes for the file in the archive
And then signer_public_key must be used to instantiate a 'blsttc' PublicKey (from bytes)
And then data_signature must be used to instantiate a 'blsttc' Signature (from bytes)
And then the blsttc PublicKey and Signature must be used to 'verify' the contents of file in the archive
And then return a response with headers 'x-data-signature-verified' (containing a boolean value to reflect the result of 'verify')

Given get_archive_binary in archive_service.rs returns all the bytes for a given path in an archive (at address)
When retrieving the bytes for a file in an archive
Then call get_archive_binary to get bytes and return them to the caller

Given verifying signatures will be required on other endpoints too
When updating get_data_archive in file_controller.rs with the verification logic
Then extract this new logic into /src/service/signature_service.rs
And define a new SignatureService struct to contain the functions
And include a 'verify' function for the new logic

Implementation Notes

- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml
- Create a copy of this issue description and save to /spec using the name of this issue as the filename (with lower underscore case, starting with the 5 char padded issue number, e.g. 00001_issue_title.txt)
- Update unit tests to validate the changes
- Don't create any new mocks!