Add Block.aload method and remove @sync_compatible from Block.load

[desertaxle]

This PR improves type hinting on Block.load by removing the @sync_compatible decorator and using @async_dispatch instead.

I had to update @async_dispatch to handle class methods and update the dispatch behavior in tasks and flows to match the behavior provided by @sync_compatible.

Also, @inject_client might be a thorn in our side because it makes wrapped functions async. To handle that in this PR, I removed @inject_client from Block.load and moved the client retrieval inside the method. There's a weird split where sometimes we can use the sync client, and other times we have to use the async client, but we can clean that up once we remove @async_dispatch.

Related to #16292

[codspeed-hq]

CodSpeed Performance Report

Merging #16341 will not alter performance

_{Comparing block_aload (972c8bc) with main (6bfce9e)}

Summary

✅ 3 untouched benchmarks

[zzstoatzz]

lgtm!

[mjpieters]

@desertaxle Why did you add this overload?

The implementation uses await on the callable argument (fn) so it must produce an awaitable, and nowhere in the prefect codebase is @inject_client used on a regular function.

[desertaxle]

Yep, you're absolutely right. I was working with @inject_client while I was making Block.load sync. This was from something that ultimately didn't work, and I forgot to remove it. I'll make a note to remove this, but feel free to remove it if you're in the neighborhood.

[mjpieters]

@desertaxle already on it 😁 See #16463.