publish to crates.io

Although cargo can use the git protocol, it may be more convenient if it can be installed on crates.io.
At the same time, llrt has not been published to crates.io. In order to prevent others from registering it first, maybe an empty package can be used as a placeholder?

Start by reviewing the repository's Cargo package metadata and its current git-protocol installation path, then check crates.io's package-name availability and publication requirements. Done means llrt can be published or a justified placeholder package is registered, with the chosen approach documented in the issue.

Written by the indexing model from the issue text.