As an AntTP user
I want to be able to provide some data for AntTP to sign using the app_secret_key over a MCP or gRPC endpoint
So that I can generate signatures for arbitrary hex data strings, which can represent data addresses using alternative APIs

Given crypto_controller.rs already exists and is used for signing data over the REST API
When adding support to sign data using MCP or gRPC API
Then use crypto_controller.rs as an example on how to integrate with crypto_service.rs for the &#39;sign&#39; function
And update crypto_handler.rs to add a &#39;sign&#39; function which is a similar format to its &#39;verify&#39; function

Given crypto.proto already exists and is used to verify signatures over gRPC
When adding support for signing data
Then update crypto.proto to include a new Sign RPC service
And update signature to be optional, to allow the same CryptoRequest/CryptoResponse messages to be used
And update crypto_handler.rs to reflect the optional signature property
And use the below as an example:

```
service CryptoService {
  ...
  rpc Sign(CryptoRequest) returns (CryptoResponse);
}

message Crypto {
  string data = 1;
  optional string signature = 2;
  bool verified = 3;
}

...
```

Given crypto_tool.rs already exists and is used to verify signatures over gRPC
When adding support for signing data
Then use crypto_controller.rs as an example on how to integrate with crypto_service.rs for the &#39;sign&#39; function
And update crypto_tool.rs to add a &#39;create_signatures&#39; function which is similar to its &#39;verify_signatures&#39; function

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
