refactor: use the lean-imt crate

refactor: add members

- Deleted the `build.rs` file, which previously handled downloading semaphore artifacts.
- Introduced a new `download_zkey` function in `utils.rs` to manage zkey downloads.
- Updated `proof.rs` to utilize the new `download_zkey` function for fetching zkeys dynamically based on tree depth.
- Added a new `witness.rs` file to handle witness dispatching based on tree depth.
- Updated `Cargo.toml` to remove `rust-witness` dependency and adjust `circom-prover` to use the latest version from the main branch.
- Added multiple witness graph binary files for different depths.

- Added a step to install the `protobuf-compiler` in the GitHub Actions workflow.
- Refactored import order in `identity.rs` for consistency.
- Adjusted import order in `group.rs` for improved readability.

refactor: remove build.rs and integrate zkey downloading into utils

Fix proof visibility

fix: fix zkey version