Some collateral damage on this one:

• Removed or made optional some wasm-pkg-common deps that don't build on wasm32-wasip1:
  • Replaced the wasm-pkg-common tokio feature flag with a broader registry-config flag which allows making more deps optional (notably etcetera)
  • Moved some functionality from wasm-pkg-common to wasm-pkg-client (the only place they were being used afaict): ContentDigest::sha256_from_file, RegistryMetadata::fetch*
• Cleaned up CI while adding wasm32-wasip1 build check
  • Reorganized steps to check cheaper things earlier
  • Renamed _local feature flag to more descriptive docker-tests
• Appease clippy

Fixes #162