crosvm: cros_async: Drain uring operations when dropping uring executor
crosvm: cros_async: Drain uring operations when dropping uring executor

Otherwise we may drop the memory that kernel still references.

BUG=b:230934649
TEST=cargo test

Change-Id: I1ab4fcc721118f744b8975d01fc907c511309585
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3625899
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Anton Romanov <7c8c28e1283c1d87f2c3df4d6b5c74b6ae02bcd9@google.com>
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm