refactor: implement automatic reflection

[JasterV]

This pull request introduces dynamic server reflection support to the granc CLI, allowing users to call gRPC services without needing a local descriptor file. The changes include new reflection client logic, CLI and core refactoring, an updated README, and build system improvements.

Server Reflection Support:

• Added a copy of the official grpc.reflection.v1 proto file to granc/proto/reflection.proto to enable dynamic schema fetching from servers that support reflection.
• Implemented logic in the core orchestration layer (granc/src/core.rs) to resolve service descriptors either from a local file or dynamically via server reflection. The CLI now works seamlessly whether or not a --proto-set is provided.

CLI and Core Refactoring:

• Moved the CLI definition to granc/src/cli.rs, now supporting an optional --proto-set, improved endpoint parsing, and conversion to the new internal core Input type.
• Refactored the core logic into granc/src/core.rs and implemented a more structured input, output and error handling, now making the core logic unit testable.

Documentation and Usability:

• Updated granc/README.md to document the new server reflection feature, clarify usage with and without descriptor files, and revise CLI argument documentation and examples. [1] [2] [3] [4] [5]

Generating a reflection service:

• Updated granc/Cargo.toml to add a gen-proto feature, declare both binaries (granc and generate_reflection_service), and manage dependencies for reflection and proto generation.
• Improved Makefile.toml with new tasks for generating the reflection service client.