fix: Fix deserialization of unions BNCH-20706

[forest-benchling]

Upstream PR: https://github.com/triaxtec/openapi-python-client/compare/main...benchling:forest-union-2?expand=1

Deserialization of unions in from_dict was not working properly, because it failed to account for cases where the union property is None or Unset. This PR adds explicit checks for None or Unset.

In addition, the type of the value to deserialize was previously set to Any, which was masking type errors. In order to fix these type errors, I introduced a new concept of check_type_for_construct for each property, which allows the type to be checked before attempting deserialization.

In the future, I think we should refine the try/except pattern; it's not good practice to rely on a catch-all except when trying to deserialize each type within the union, because we don't know what exception was actually raised.

Follow-ups:

• https://benchling-jira.atlassian.net/browse/BNCH-20742
• https://benchling-jira.atlassian.net/browse/BNCH-20743

NOTE: This fails openapi-specs tests, because it's dependent on fixing https://benchling-jira.atlassian.net/browse/BNCH-20726.

[bowenwr]

Geez, thanks for working through this. Let's figure out a way today to get everything merged in, re-baseline the fixes branch and see if we can get everything stable again but feature complete.

[forest-benchling]

@packyg I'm gonna merge this in the interest of time and avoiding juggling too many balls at the last minute. It would still be great if you could take a read of it when you have time, for context.