Include generics in discriminated union schemas

[tpoliaw]

• Restrict subclasses of typed unions
• Allow arbitrary types to be included in 'StrictConfig' types

Fixes #156

Instructions to reviewer on how to test:

1. Create set of subclasses of a decorated base class:

@discriminated_union_of_subclasses
class Base(Generic[T]):
    pass

@dataclass
class Child(Base[T]):
    foo: T

2. Try and deserialise a serialised Child as a Base:

one = TypeAdapter(Base[int]).validate_python({"type": "Child", "foo": "42"})
assert one.foo == 42 # <== 42 instead of "42" as type should be converted

Checks for reviewer

• Would the PR title make sense to a user on a set of release notes

[coretl]

From a skim this looks fine to me

[DiamondJoseph]

A nit and a possible edge case

[DiamondJoseph]

Could left.__ be a subset of right.__?

class Super:
class Sub(Super):

@discriminated...
class Parent(Generic[Super]):
class Child(Parent[Sub], Generic[Sub])

e.g. for class ReadableMovable(Movable)?

[tpoliaw]

You can't pass concrete types to Generic as in this example but yes, this is definitely restricting the supported cases beyond what is possible in theory. It turns out to be difficult to determine what should be passed without re-implementing an entire type-checker. There are a couple of examples in #156 and a few in a previous version of this commit where I tried to support a wider range of options but until we have a use case for them I'd prefer a well defined restriction instead of an array of unsupported edge-cases.

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.70%. Comparing base (b75ff5d) to head (216f797).

Files with missing lines	Patch %	Lines
src/scanspec/core.py	95.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #157      +/-   ##
==========================================
- Coverage   95.74%   95.70%   -0.05%     
==========================================
  Files           9        9              
  Lines         940      977      +37     
==========================================
+ Hits          900      935      +35     
- Misses         40       42       +2     

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[callumforrester]

Delete uncovered lines as discussed

[callumforrester]

Should consider adding a codecov config like ophyd-async's for consistency

[DiamondJoseph]

Rebased to pick up codecov changes