fix(memtables): track memtables with a weakset to allow overwriting tables with the same name but different data

[cpcloud]

Description of changes

Fixes an issue with memtable name reuse where we were never overwriting
memtable data in the backend, even if the data changed and the name remained
the same.

The solution I came up with here was to add a weakref.WeakSet to track
memtable ops, which are hashed based on the data-containing object.

The reason a WeakSet is necessary is to preserve the drop-on-unreachable
semantics of memtable.

Issues closed

Closes #10131.

[cpcloud]

I know that previously we decided against using con.list_tables() but I think it reflects the specific UX we want for memtables here, and avoids mucking around in implementation details of how exactly memtables are stored, collected and dropped.

[cpcloud]

That said, I think we'll want to adjust this test to use list_temp_tables() once that lands.

[cpcloud]

Clouds passing:

…/ibis on  memtable-set is 📦 v9.5.0 via 🐍 v3.12.5 via ❄️   impure (ibis-3.12.5-env)
❯ pytest -m bigquery -n auto --dist loadgroup --snapshot-update -q && pytest -m snowflake -n 8 --dist loadgroup --snapshot-update -q
bringing up nodes...
..........s.s.............s...............s...........x.x.................sssssssssssssssssssss.ssssssssssssssss [  5%]
sssssssssssssssssssssssssssssssssssssssssss.sssssssssssssssssssssssssssssssssssssssss.......x..............xx... [ 10%]
.......s..x...............................s......................x.............................................. [ 15%]
..............x...................xx....x............x..........x.............................x.xxxx..x..xxx.x.. [ 20%]
...xx.xx.x.x.x.xxx.xx....xxx.xx.xxxxx.x.x..xx.x.x.....xx..........x...x..........x..x......x...xx.x....xx.x....x [ 25%]
..x.........x..........x.......x.....x..............xx.x......................x..............x...xx.....x...x... [ 30%]
.....x......x..........x...................x.......x........................x.x............x...x..x.......x..... [ 35%]
....................................sx...............x.x..x..s...............s.......s......s.x.......x......... [ 40%]
.x.....x..........x..x.....xx...x.....x......x..x........................x..x......x.x...........xx...xx...x.... [ 45%]
....x.x......xx.X........x...x...x....x.x.....x....x.x..x....x.........x.x..X...xx.x.xXx.x..x......xx..xx....... [ 50%]
xx..x........x.........xX.x......x....xx.........................x......x....x......xx..............xx.x.x....xx [ 55%]
..x.x..x....x........x.....x....xx..x.x.....................x.xxx..xx......x...x....x.xxxxxxxx.xxxxxxx..xxxxx.xx [ 61%]
xxxxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxxxxx.xxxxxx.xxx.xxxxxxxxxxxx.x.xxxxxxxxxxxxxxxxxx.xxxxxxxxxxxxxxxxx....x..x [ 66%]
.xx.x............x.............x..................................x.x.....x.xx..........................x.....x. [ 71%]
..............x.......xxxxxxxxxxxx....................x.......................x..x........x.x.x..x.............. [ 76%]
......x..............................x...x........x.....x...x..xx.x......x...................x.................. [ 81%]
.................x..........x...........x....................................................................... [ 86%]
...............................................................x................................................ [ 91%]
................................................................................................................ [ 96%]
..x.............x.........................................................                                       [100%]
1715 passed, 132 skipped, 351 xfailed, 4 xpassed in 395.85s (0:06:35)
bringing up nodes...
......xxx...xx.x.....xxx.x.x.xxxx...x..........................................x.....x.......................... [  5%]
..................................x.x....................x.x.......x.......x..x......x...............x....xxx.x. [ 11%]
.....................x..x.............x...x......xx....x...x..............................x..................x.. [ 17%]
....................................x..x........xx........................x....x..........x.......xx............ [ 22%]
x....x.....xx.........................x....................x.x.x...................................x............ [ 28%]
................xx.......xx...x...xx.....x.........s...............x...........................................x [ 34%]
..........................x..................x.......x....................x.........x..........x................ [ 39%]
......................................x.............................x..x.xx.x.x.xx....x..xx.....x..x.xxx...xxx.x [ 45%]
x..xxx.xx.x.xx.x..xx.......x.x.xx..x...x..x.x..xxxxx..x.x..xx.....xxx.x.xxxxx.x....xx...x........x...x.......... [ 51%]
......x...x..............x....x.......x.............x.....xx......x..................xxx.....x....x............. [ 56%]
........x....x..........x...x.......xx..x..x..x.........x...x.x..x..x.............x............................. [ 62%]
..x.......xx.x..........................................................................s........x.........x.... [ 68%]
...x...x.........................................x.......x.....xx....x.......x....xx..................xxx..xxx.. [ 73%]
...x.....x..x.x...x..x..x.......x..........x.x....x..xx..x.xx.x..x.x..x............x.....x................x..s.. [ 79%]
s.............................................................s..................x.............s....x........... [ 85%]
..................xxxxxxxx.x.x.x...x.........................................x.........x..................s..... [ 90%]
......s......................................................................................................... [ 96%]
....................................................s..............s.                                            [100%]
1733 passed, 10 skipped, 230 xfailed in 200.23s (0:03:20)

[jcrist]

I think we can reduce this state to just a single weakset and dict, mind if I push up a commit?

[cpcloud]

Go for it!

[cpcloud]

@jcrist I am still open to you pushing up a commit if you've already got it locally, otherwise, no big deal.