[Feature Request]: Support generic PTransforms in Python SDK

### What would you like to happen?

It would be awesome for the following code to work (written in 3.12 syntax, but would be great in <=3.11 syntax too)

```
T = TypeVar("T")

@dataclass.dataclass()
class NeatOutputClass[T]:
data: T

class ReusableTransform[T](beam.PTransform):
def __init__(self, value_extractor: Callable[[Any], T):
# This is a bit contrived, but not unreasonable for a transform acting
# on slightly different data. Could be done as a generic DoFn too.
self.value_extractor = value_extractor

def expand(self, pcoll: beam.PCollection) -> NeatOutputClass[T]:
# Overly simplified for simple reproducibility.
return pcoll | beam.Map(lambda x: self.value_extractor(x))
```

But unfortunately this yields `TypeError: Subscripted generics cannot be used with class and instance checks`

Full Stack Trace

```py
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/transforms/ptransform.py:622: in __ror__
result = p.apply(self, pvalueish, label)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/pipeline.py:754: in apply
pvalueish_result = self.runner.apply(transform, pvalueish, self._options)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/runners/runner.py:191: in apply
return self.apply_PTransform(transform, input, options)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/runners/runner.py:195: in apply_PTransform
return transform.expand(input)
my_repo/transformation.py:263: in expand
pcolls
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/transforms/ptransform.py:622: in __ror__
result = p.apply(self, pvalueish, label)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/pipeline.py:757: in apply
transform.type_check_outputs(pvalueish_result)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/transforms/ptransform.py:475: in type_check_outputs
self.type_check_inputs_or_outputs(pvalueish, 'output')
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/transforms/ptransform.py:496: in type_check_inputs_or_outputs
if hint and not typehints.is_consistent_with(pvalue_.element_type, hint):
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:1323: in is_consistent_with
return base._consistent_with_check_(sub)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:711: in _consistent_with_check_
len(sub.tuple_types) == len(self.tuple_types) and all(
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:712: in
is_consistent_with(sub_elem, elem) for sub_elem,
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:1323: in is_consistent_with
return base._consistent_with_check_(sub)
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:271: in _consistent_with_check_
is_consistent_with(sub.inner_type, self.inner_type))
/home/vscode/.cache/pants/named_caches/pex_root/venvs/s/192fb705/venv/lib/python3.11/site-packages/apache_beam/typehints/typehints.py:1329: in is_consistent_with
return issubclass(sub, base)
```

### Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

### Issue Components

- [x] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam YAML
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Infrastructure
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner