Such that decoded output equivalent to `str|None` can actually be
unpacked from a `type_names = ['str', 'NoneType]` without just
ignoring the null-type entry.. Previously, the loop would fall through
silently ignoring the `None` -> `NoneType` string representation mapped
by `.enc_type_union()` and the output union would be incorrect.
Deats,
- include the stdlib's `types` in the lookup loop, obvi changing the
output var's name to `_types` to not collide.
- add output checking versus input `type_names` such that we raise
a value-error with a case specific `report: str` when either,
* the output `_types: list[Type]` is empty,
* the `len(_types) != len(type_names)`.
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