Fix bug flushing Data frames from asyncio client

[coretl]

When AsyncioClient.data() was called with non-zero flush_period then it only yielded the Data after flush when a new packet of data appeared on the wire or at the end of acquisition. This changes it to be more eager and yield as soon as it is flushed.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03% 🎉

Comparison is base (e24fdfc) 96.37% compared to head (4ebc66a) 96.41%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #56      +/-   ##
==========================================
+ Coverage   96.37%   96.41%   +0.03%     
==========================================
  Files          12       12              
  Lines        1160     1198      +38     
==========================================
+ Hits         1118     1155      +37     
- Misses         42       43       +1     

Files Changed	Coverage Δ
pandablocks/asyncio.py	97.87% <100.00%> (-0.19%)	⬇️

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[dmgav]

@coretl I just tested the code with PandABox and PandA IOC. Panda was configured to generate 12 trigger pulses, which resulted in 12 data points saved to HDF5 file. So this seems to fix the original issue. But now I see the following error message (IOC remains functional):

INFO:Arming PandA
INFO:Opened '/nsls2/users/dgavrilov/panda-test/panda_data_20230901_110824.h5' with 16 byte samples stored in 3 datasets
INFO:Requested number of frames (12) captured, disabling Capture.
INFO:Closed '/nsls2/users/dgavrilov/panda-test/panda_data_20230901_110824.h5' after writing 12 samples. End reason is 'Ok'
ERROR:_GatheringFuture exception was never retrieved
future: <_GatheringFuture finished exception=CancelledError()>
Traceback (most recent call last):
  File "/nsls2/users/dgavrilov/conda_envs/2023-2.1-py310-tiled-panda/lib/python3.10/asyncio/tasks.py", line 605, in sleep
    return await future
asyncio.exceptions.CancelledError

During handling of the above exception, another exception occurred:

asyncio.exceptions.CancelledError
INFO:Disarming PandA

[coretl]

@dmgav does this work for you now? Should I merge?

[dmgav]

Yes, position capture works now without issues.