Inline dependency-versions syntax

[joerick]

To help with #2002, I propose a way to specify dependency version constraints inline, without the extra file. This would eliminate the need for an additional CIBW_PYODIDE_BUILD_VERSION option, while being consistent with our existing version management system.

This would allow setting the pyodide-build version like:

CIBW_DEPENDENCY_VERSIONS_PYODIDE: "packages: pyodide-build==0.29.1"

So far, no implementation yet, just docs for discussion.

[joerick]

Having reviewed #2002 again, I think this would be a useful feature. Specifically, there's a check for compatible versions between pyodide and pyodide-build - if we provide an option for CIBW_PYODIDE_VERSION, and we don't have this, changing pyodide version becomes a bit hassle, because you need to make a constraints file as well.