cloud versioning: slow

Part of #7995

Description

Cloud versioning is working much slower than traditional remotes

Reproduce

$ git clone [e-mail]:iterative/example-get-started.git
$ cd example-get-started
$ dvc pull
$ dvc remote add -f -d cloud s3://mybucket/remote
$ time dvc push
8 files pushed
dvc push  0.71s user 0.17s system 13% cpu 6.626 total
$ dvc remote modify cloud version_aware true
$ dvc remote modify cloud worktree true
$ time dvc push
Updating lock file 'dvc.lock'
Updating lock file 'dvc.lock'
9 files pushed
dvc push  0.98s user 0.21s system 6% cpu 17.443 total

[dberenbaum]

In the time it takes to complete a regular dvc push or aws s3 sync of a large directory, dvc push to a cloud-versioned remote hangs and shows no output (even with -v) and makes no progress that I can tell. Tested with the contents of s3://dave-sandbox-versioning/coco/test2014.

[dberenbaum]

Results for a slightly larger dataset.

With cloud versioning:

$ time dvc push
6946 files pushed
dvc push  97.23s user 16.91s system 8% cpu 23:39.43 total

$ time dvc pull
M       test2014/
1 file modified and 6946 files fetched
dvc pull  66.84s user 21.57s system 11% cpu 13:00.08 total

Without cloud versioning:

$ time dvc push
6947 files pushed
dvc push  50.29s user 8.22s system 21% cpu 4:35.87 total

$ time dvc pull
M       test2014/
1 file modified and 6946 files fetched
dvc pull  22.32s user 8.36s system 33% cpu 1:30.41 total

I can follow up with profiling for each.