Make thrust nosync execution policy the default thrust policy

[abc99lr]

Testing. Do not merge.

Based on the discussions from #2293, it's a good idea to test if we could use nosync thrust calls by default. This PR changes the current rmm::exec_policy to its async version rmm::exec_policy_nosync.

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[abc99lr]

Tagging @cjnolet to enable testing

[cjnolet]

@abc99lr for future reference, you should be in the rapids org and the raft-triage group. The reason CI isn't automatically starting on this PR is because you haven't signed your commits. This is something you should be able to set up once and it'll "just work" on your dev system going forward. Here's the instructions to do this.

[cjnolet]

/ok to test

[abc99lr]

It seems this PR fails pr / conda-cpp-tests / tests (amd64, 3.11, 12.2.2, ubuntu22.04, v100, latest) (push). But I checked the log and all the status show success. Should we rerun the CI? Or maybe I missed something?

Here is the link to the log.
https://github.com/rapidsai/raft/actions/runs/9024355165/job/24800696954?pr=2302

[cjnolet]

@abc99lr yeah it's weird indeed. i"m rerunnig that test checker. It's possible it could have been a chance occurrence.

[cjnolet]

/merge