Hack in `unshardedSizes` can cause inconsistent values for the same extent `Val*`

[zasdfgbnm]

As demonstrated in #5708, The same extent Val* could have different multiplier. This is a blocker for my PR #5082, because this could lead to PrecomputedValues binding the same Val* with different value for the same instance of FusionExecutorCache.

Any suggestion? cc: @wujingyue

[wujingyue]

I've yet to understand why

Fuser/csrc/multidevice/execution_utils.cpp

Line 73 in 878c3e2

// TODO(#5525): hack for MultiDeviceExecutor. MultiDeviceExecutor looks

can create problems.

I failed to reproduce this reliably. I suspect it has something to do with the use of static: https://github.com/NVIDIA/Fuser/pull/5708/files#diff-140da8af7df6a9ae6ddfbc972a5db1bfdd0efba4b6412902f285b32f3d131347R72. Some Val*s from a previous test might have stayed in the hashtable even though they've been deleted.