Move `v1` artifacts into dedicated package/file

[gbrgr]

I think it'd be a good idea to move older artifacts (such as the v1 exec_v1) into a dedicted package compat so that users can write

from railib.compat.v1 import exec

instead of explicitly naming exec_v1. This allows developers to adapt their legacy code depending on older versions of this SDK.

Thoughts @bradlo @NRHelmi?

[billscheidel-rai]

Note: This issue has been migrated to https://relationalai.atlassian.net/browse/RAI-6464.

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