Improve consistency of sync_compatible when running flows in remote environments

[desertaxle]

This PR ensures that functions wrapped in @sync_compatible execute as expected in remote environments by setting RUNNING_ASYNC_FLAG to False when running a sync function in a worker thread. Flow scripts are loaded in a worker thread without an event loop, so updating the RUNNING_ASYNC_FLAG context variable will ensure those wrapped async functions execute as sync.

I noticed that a couple of threads are created when loading a flow script. The number of created threads could be reduced by creating a sync implementation of load_flow_from_flow_run, but we'd likely still need to call storage block methods and pull steps in a separate thread since they are async by default.

Closes #14625

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[codspeed-hq]

CodSpeed Performance Report

Merging #14660 will not alter performance

_{Comparing sync-compatible-remote (cde51ec) with main (e091528)}

Summary

✅ 5 untouched benchmarks

[zangell44]

Love the regression test!