eryx-precompile compile: auto-download runtime.wasm when input omitted

[sd2k]

Summary

eryx-precompile compile currently requires an explicit runtime.wasm path as a positional argument. For the common case where you just want to customize compilation options (e.g. --target x86-64-v3, --preinit, --package), it would be nice to omit the input and have it auto-download the matching runtime.wasm from GitHub Releases — the same way setup does.

Example

# Currently required:
eryx-precompile compile runtime.wasm -o runtime.cwasm --preinit --stdlib ./python-stdlib --target x86-64-v3

# Proposed: omit input, auto-downloads runtime.wasm
eryx-precompile compile -o runtime.cwasm --preinit --stdlib ./python-stdlib --target x86-64-v3

Suggested behavior

• If no positional input argument is provided, download runtime.wasm from the GitHub Release matching the binary's version (reusing the download_runtime_wasm logic from setup)
• Cache the downloaded wasm in ~/.cache/eryx/ to avoid re-downloading
• If input is provided, use it as-is (current behavior, no change)