bpo-44337: Shrink the LOAD_ATTR/STORE_ATTR caches

[brandtbucher]

One adaptive entry is enough.

https://bugs.python.org/issue44337

[sweeneyde]

LGTM. Can't the same idea shrink LOAD_METHOD from 3 entries down to 2? Then _PyAttrCache can be eliminated altogether.

[markshannon]

Can't the same idea shrink LOAD_METHOD from 3 entries down to 2? Then _PyAttrCache can be eliminated altogether.

I was looking at LOAD_METHOD yesterday, and it needs 3 slots of data for Python methods. It needs the type version, the shared dict-keys's version and a pointer to the Python function, in addition to the count and original oparg. We could try using 16 bits for one of the versions, saving a slot at the cost of more specialization failures.

[markshannon]

Looks good.
Can you rename dk_version_or_hint to dk_version as we no longer use it as a hint.
Feel free to merge once you've done that.