bpo-40116: Add insertion order bit-vector to dict values to allow dicts to share keys more freely.

[markshannon]

See faster-cpython/ideas#30 (comment)

https://bugs.python.org/issue40116

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @markshannon for commit 8214006 🤖

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[markshannon]

No significant performance change https://gist.github.com/markshannon/814e38650cbe4ba1639e31294d4879e6

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @markshannon for commit 51c1ec8 🤖

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[markshannon]

Despite providing no speedup, I'd like to merge this, as it enables compact objects.
Work-in-progress implementation of compact objects here: https://github.com/faster-cpython/cpython/tree/inline-attributes-with-opt (there are a few leaks that I need to hunt down, and some general cleanup to be done).

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @markshannon for commit 2a13a2d 🤖

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[markshannon]

The build bot failures are cancellations (presumably timeouts).

[markshannon]

I'm merging this now as I have https://github.com/faster-cpython/cpython/tree/inline-attributes-with-opt working and it shows measurable speedups as well as reduced memory consumption.

[methane]

I noticed that this change may break order of merged dict.