Fix handling for poll calls to non-generator futures

[JustusAdam]

What Changed?

No longer attempts to use the "resolve original arguments" kind of async handling on futures that have explicit poll implementations, as opposed to being auto-implemented (e.g. async fn and async blocks).

Removes a loop in async arg resolution, as it was no longer exercised.

Why Does It Need To?

Avoids spurious errors in trying to resolve async arguments.

Fixes #159

Checklist

• Above description has been filled out so that upon quash merge we have a
  good record of what changed.
• New functions, methods, types are documented. Old documentation is updated
  if necessary
• Documentation in Notion has been updated
• Tests for new behaviors are provided
  • New test suites (if any) ave been added to the CI tests (in
    .github/workflows/rust.yml) either as compiler test or integration test.
    Or justification for their omission from CI has been provided in this PR
    description.