Remove restrictions on inheriting partial'd configs

[rsokl]

There are restrictions on inheritance patterns permitted by builds. Specifically, one could not inherit from a PartialBuilds-type config without explicitly "opting-in" and specifying zen_partial=True on the child. And even in this latter case, one could not include zen-processing features (such as zen_meta) in the child config.

See #289 for a detailed discussion of these restrictions.

This PR lifts all of these restrictions!

Before:

The default value for zen_partial was False. There was no way for a user to inherit from a partial-builds config and produce a builds-config

parent_with_partial = builds(int, zen_partial=True)

builds(int)  # Type[Builds[Type[int]]]
builds(int, builds_bases=(parent_with_partial,)) # Not allowed
builds(int, zen_partial=False, builds_bases=(parent_with_partial,)) # Not allowed
builds(int, zen_partial=True, builds_bases=(parent_with_partial,)) # Type[PartialBuilds[Type[int]]]
builds(int, zen_partial=True, builds_bases=(parent_with_partial ,), zen_meta=dict(a=1))  # Not allowed (child uses zen-processing features)

After:

The default value for zen_partial is now None. Specifying zen_partial explicitly will determine whether the resulting config is a partial-builds, otherwise it is inherited or defaults to False

parent_with_partial = builds(int, zen_partial=True)

builds(int)  # Type[Builds[Type[int]]]
builds(int, builds_bases=(parent_with_partial,)) # Type[PartialBuilds[Type[int]]]
builds(int, zen_partial=False, builds_bases=(parent_with_partial,))  # Type[Builds[Type[int]]]
builds(int, zen_partial=True, builds_bases=(parent_with_partial,)) # Type[PartialBuilds[Type[int]]]
builds(int, zen_partial=True, builds_bases=(parent_with_partial,), zen_meta=dict(a=1))  # Type[PartialBuilds[Type[int]]]

It achieves this by changing the default value of builds(..., zen_partial) to be None instead of False.

• None indicates that the config will not entail partial instantiation unless that behavior is inherited
• False indicates will not entail partial instantiation under any circumstances

make_config will now also raise when the following patterns are detected in a config:

• _zen_target is specified but _target_ does not point to hydra_zen.funcs.zen_processing. This indicates a multiple inheritance pattern that "clobbers" the zen-processing configuration pattern
• _partial_=True is specified in conjunction with zen-processing patterns

To-Do:

• Add error handling in make_config when inheriting _partial_=True and _zen_partial=True fields simultaneously
• Provide public function for checking is_partial and/or validate_partial so that users can inspect whether or not a config is a partial config without needing insights into the two different protocols for partial configs.

Closes #289
Closes #288

[rsokl]

@jgbos would you mind reviewing this / working off this branch during your day-to-day (if you aren't already) to confirm that you don't hit bugs? I still have some lingering to-dos, but they are relatively minor compared to the rest of this PR

[jgbos]

@rsokl fyi, I haven't been running into any issues with the branch all week (I haven't done a lot though).

[rsokl]

@jgbos great! I plan to try to tackle the outstanding To-Dos when possible and then merge this