Consolidate CLIs into a single `eryx` binary

[sd2k]

Summary

Currently there are two CLI binaries:

• eryx-precompile — pre-compiles WASM runtimes, will gain a setup command (Add eryx-precompile setup command for crates.io users #99)
• The Python eryx CLI (__main__.py) — REPL, script execution, etc.

It would be nice to consolidate into a single eryx CLI (Rust binary) with subcommands, e.g.:

eryx run script.py          # execute a script
eryx repl                   # interactive REPL
eryx setup                  # download + pre-compile runtime (from #99)
eryx precompile             # advanced: precompile from local wasm

Considerations

• The Rust CLI could replace the Python __main__.py entry point
• Would need feature parity with the Python CLI (REPL, streaming output, volumes, callbacks, etc.)
• cargo-dist would build this single binary instead of eryx-precompile
• cargo binstall eryx would give users both the library and the CLI tool