Support sync functions that return awaitables

[coretl]

E.g. lambda value: async_func(value)

Also fix some mypy issues

Fixes https://github.com/dls-controls/aioca/issues/32

[codecov[bot]]

Codecov Report

Merging #33 (8064d58) into master (777dab1) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #33   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          422       428    +6     
=========================================
+ Hits           422       428    +6     

Impacted Files	Coverage Δ
aioca/_catools.py	100.00% <100.00%> (ø)

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