refactor: remove once_cell dependency

[jingyun19]

Remove once_cell deps now that the once_cell::sync::OnceCell functionalities are in std::sync::OnceLock

Built and tested with cargo build and cargo test.

Issue: #90

[rrevenantt]

This crate is in the process of being merged to upstream antrl4. Current work is being done in the https://github.com/antlr4rust/antlr4 so please create PR there. Eventually it will be a part of main antlr4 repository

[jingyun19]

thanks for the heads up! After the merge, do we need to update the cargo in our codebase?

[rrevenantt]

You mean update dependency version in Cargo.toml? Not sure. I guess, as usual, only if you want bugfixes/improvements.