Reduce async overhead due to auto_await

[mohd-akram]

The types of most rendered values tend to be primitives, so we can avoid a costly call to inspect.isawaitable for them. This improves performance by at least 15% in my tests.

• fixes Async is slow due to isawaitable use #1514

Checklist:

• Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• Add .. versionchanged:: entries in any relevant code docs.
• Run pre-commit hooks and fix any issues.
• Run pytest and tox, no tests failed.

[mohd-akram]

@davidism Have you had a chance to look at this?

[davidism]

No not yet. When I do, I'll leave a review, comment, or merge and you'll get a notification.