Bump to 1.4.3

[pepoluan]

What do these changes do?

Mostly, version bumping.

Also some fixings for tox. Notably, taking out pytype.

Are there changes in behavior for the user?

None

Related issue number

None directly

Checklist

• [x] I think the code is well written
• [x] Unit tests for the changes exist
• [x] tox testenvs have been executed in the following environments:
  • [x] Windows 10: qa, docs
• [x] Documentation reflects the changes
• [x] Add a news fragment into the NEWS.rst file

[codecov[bot]]

Codecov Report

Merging #328 (dff1d3d) into master (c78fc95) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #328   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1691      1696    +5     
  Branches       314       310    -4     
=========================================
+ Hits          1691      1696    +5     

Impacted Files	Coverage Δ
aiosmtpd/__init__.py	100.00% <100.00%> (ø)
aiosmtpd/smtp.py	100.00% <100.00%> (ø)
aiosmtpd/handlers.py	100.00% <0.00%> (ø)
aiosmtpd/controller.py	100.00% <0.00%> (ø)
aiosmtpd/proxy_protocol.py	100.00% <0.00%> (ø)

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