Ensure type is passed through _io.sync

[jacobtomlinson]

Use a generic class type to ensure type hints work correctly on classes decorated with @sync.

xref #381

Before

from kr8s.objects import Pod

# Type checker shows `pod` as `Any`
pod = Pod("kube-apiserver", namespace="kube-system")

# Assisting the type checker does not work, `pod` is still recognized as `Any`
pod: Pod = Pod("kube-apiserver", namespace="kube-system")

After

from kr8s.objects import Pod

# Type checker shows `pod` as `Pod` even without the assistance
pod = Pod("kube-apiserver", namespace="kube-system")

cc @marcodlk

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 92.30769% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.22%. Comparing base (87063fc) to head (e8d75ad). Report is 100 commits behind head on main.

Files	Patch %	Lines
kr8s/_io.py	92.30%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #384 +/- ## ========================================== + Coverage 94.61% 95.22% +0.60% ========================================== Files 29 29 Lines 3141 3416 +275 ========================================== + Hits 2972 3253 +281 + Misses 169 163 -6 ```

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