feat(kona-host): export HostCli, fix compilation

[ratankaliani]

The modules defined in main.rs are not accessible outside the crate because main.rs is the binary entry point, not a library file. By default, code in main.rs is only available within the binary itself.

To make the CLI types (e.g. HostCli) available externally (e.g. in https://github.com/succinctlabs/op-succinct), they need to be:

• Defined in lib.rs (or a module exported by lib.rs).
• Marked with pub visibility.

Once I included exposed the modules in lib.rs, modules within cli, single, etc., need to import types from kona-host with crate::.

[ratankaliani]

If we want to restrict the accessible types from these crates, happy to apply the pub use pattern above.

[ratankaliani]

@clabby Would it be possible to export SingleChainHostCli from kona-host? Or was this the intended behavior for it to only be used by binaries in kona-host?