This commit updates the README files for the `core:api`, `core:model`, and `core:proto` modules to improve documentation and reflect current usage.
Key changes include:
- Bumping the library version to `v2.7.13` in usage examples.
- Adding a detailed README for the `core:proto` module.
- Updating the `core:api` README to use `MeshtasticIntent` constants instead of hardcoded strings.
Signed-off-by: James Rich <2199651+jamesarich@users.noreply.github.com>
