add flush to TCPIP SOCKET

[dkriegner]

This PR attempts to add support for the flush operation of TCPIP Sockets.

For Sockets the read buffer operations of flush seem to be equal to clear. Since the writing to the sockets is blocking it seems no write buffer operations are possible/needed.

• [ ] Related to #348 for TCPIP sockets
• [x] Executed black . && isort -c . && flake8 with no errors
• [ ] The change is fully covered by automated unit tests
• [x] Added an entry to the CHANGES file

[dkriegner]

I would need some feedback on the proposed changes and in particular the comment above about the discard/flush of the write buffer.

Of course this PR would not fix #348 but hopefully improve the situation

[MatthieuDartiailh]

I will need to dive a bit in the VISA spec to answer this meaningfully so it may take me some time. Ping me if you see nothing by mid-February.

[codecov-commenter]

Codecov Report

Merging #350 (b72126f) into main (8a0753b) will decrease coverage by 0.69%. The diff coverage is 33.33%.

:exclamation: Current head b72126f differs from pull request most recent head f057e35. Consider uploading reports for the commit f057e35 to get more accurate results

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@@            Coverage Diff             @@
##             main     #350      +/-   ##
==========================================
- Coverage   23.13%   22.44%   -0.69%     
==========================================
  Files          22       21       -1     
  Lines        3277     3226      -51     
  Branches      450      447       -3     
==========================================
- Hits          758      724      -34     
+ Misses       2501     2484      -17     
  Partials       18       18              

Flag	Coverage Δ
unittests	22.44% <33.33%> (-0.69%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pyvisa_py/tcpip.py	20.73% <33.33%> (+0.14%)	:arrow_up:

... and 8 files with indirect coverage changes

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[MatthieuDartiailh]

Sorry for the slow responses. Could you rebase on latest main ? I will try to merge quickly once it is done

[dkriegner]

I fixed the merge conflict. you prefer a real rebase (with a force push)?

[MatthieuDartiailh]

Usually yes but that's fine.