Introduced a new `SignatureCacheService` class to handle
cached signatures via API interactions. This includes methods
for saving, retrieving, and deleting signatures using `HttpClient`.
- Added dependency injection for `HttpClient` and `IOptions<ApiOptions>`.
- Implemented `SaveSignatureAsync`, `GetSignatureAsync`, and
`DeleteSignatureAsync` methods with error handling.
- Utilized `Uri.EscapeDataString` for safe URL encoding.
- Added support for HTTP operations with `System.Net.Http.Json`.
