In the previous version it was adding the extra packages as
`propagatedBuildInputs`. This meant that this package would be rebuild
for no reason (it is not like the package will actually depend on the
extra inputs) and also cause the strange side-effect of creating a hy
package without its console entry-points (e.g.: no `$out/bin` contents).
Now we are reusing the `python.withPackages` that will avoid the
unnecessary rebuild, fixing both issues.
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