Support contextmanagers as assets

[sneakers-the-rat]

Part of #110 but doesn't close it.

This is the first half of the issue, allowing contextmanagers as assets, but it does not address the main point of the issue, which is about providing some kind of "middleware" that can wrap around nodes for repeated operations across nodes.

This PR just makes it possible to use contextmanagers as assets, simple as.

however during testing, discovered a few bugs in how assets were handling both in the base runner and the async runner:

• The base runner was not passing edges to the state when initializing node-scoped assets, so all node-scoped assets were initialized every time (bad)
• The logic in state was flawed to allow that to happen - we should only initialize node-scoped assets when they are directly depended on by the node.
• async runner double-initialized node-scoped assets, and didn't deinit process-scoped assets.

These were discovered here because the test for the contextmanager included init/deinit counts, which were off in the flawed code. the tests here do not test global counts of init/deinit, just per asset instance, so further testing to constrain the behavior would be good here.

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📚 Documentation preview 📚: https://noob--246.org.readthedocs.build/en/246/

[coveralls]

coverage: 84.711% (+0.1%) from 84.589% — issue-110 into main

[codspeed-hq]

Merging this PR will not alter performance

✅ 8 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing issue-110 (e8449d9) with main (5c236d7)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩