Updating risc0 dependency versions requires updates in multiple places

[nategraf]

When updating the zkVM version, it requires updates to a number of places in client applications (e.g. applications based on the Foundry template). It would be good to simplify this experience. Versions needs to be kept in sync across.

• Workspace root Cargo.toml.
• Guest workspace Cargo.toml.
• Installed cargo-risczero version.
• risc0-ethereum git submodule.
• .gitmodules file (if a branch is set).
• CI job definitions.

It would be good to simplify this picture, with the most ideal version being to have the references to risc0 crates in the workspace root Cargo.toml, and have everything else consume the version specified there.