RFC 2: partial lockfiles

As proposed by @bollwyvl https://github.com/pyodide/pyodide-lock/issues/4#issuecomment-1608118850

The way the in-flight jupyterlite PR works is by:

• generating partial lockfiles
  • these wouldn't be sufficient to run anything
• layering them, by name, on top of the as-loaded runtime with whatever index is hosted with it
  • this could be hoisted/normalized in pyodide's initializer with e.g. extraLockUrls: []
    • this could be non-destructive, which might be better, and potentially support "punch-out" by setting a name to a null (ick!)

The concrete things this solves there:

• auto-install-on-import
• replacing packages in the pyodide stdlib
  • IPython has an optional dependency on jedi/parso (but still downloads them)
    • we haven't been able to make jedi work well enough in jupyterlite to use, so would rather replace it with dummy shims to save a couple megabytes on the wire
  • per-PR docs builds of packages that are in the pyodide stdlib and really just want one different

Alternative proposals: https://github.com/pyodide/pyodide-lock/issues/8 https://github.com/pyodide/pyodide-lock/issues/10

Start by reading the linked jupyterlite PR and the referenced pyodide-lock issues, then inspect how the pyodide initializer currently loads lockfiles. The issue needs a settled design for partial lockfile layering and explicit acceptance criteria before implementation can be considered done.