Remove eval_bytecode from default plugin and update namespace

[jeffcharles]

Description of the change

Removes the exported function named eval_bytecode from the default plugin and updates the namespace of the plugin since this is a breaking change. Also removes run_bytecode from the public API of the javy-plugin-api crate.

Why am I making this change?

We'll be changing the default plugin API substantially as part of implementing the new plugin API RFC anyway. I also want to reduce the size of that PR.

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli, javy-plugin, and javy-plugin-processing do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.