Make forwardmodelrunner async

[jonathan-eq]

Issue
Resolves #9041

Approach
We will get a lot of those errors from the forward model runner (compute cluster) when we forcefully signal kill, and dont let it shut down gracefully (a lot of those errors are due to websocket connection being suddenly dropped, and not closed). Making it async would allow us to early return from the runner's run_method by calling Task.cancel on it, and we could do some cleanup on asyncio.CancellationError.

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'pytest tests/ert/unit_tests -n logical -m "not integration_test"')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Create Backport PR to latest release