Use python 3.9

[codecov[bot]]

Codecov Report

Merging #641 (fc2433c) into main (41ace49) will increase coverage by 0.09%. The diff coverage is 84.37%.

@@            Coverage Diff             @@
##             main     #641      +/-   ##
==========================================
+ Coverage   64.50%   64.60%   +0.09%     
==========================================
  Files          16       16              
  Lines        1854     1859       +5     
  Branches      497      497              
==========================================
+ Hits         1196     1201       +5     
  Misses        556      556              
  Partials      102      102              

Impacted Files	Coverage Δ
ord_schema/macros/workups.py	0.00% <0.00%> (ø)
ord_schema/scripts/parse_uspto.py	0.00% <0.00%> (ø)
ord_schema/macros/solutions.py	97.36% <100.00%> (ø)
ord_schema/message_helpers.py	85.63% <100.00%> (+0.03%)	:arrow_up:
ord_schema/resolvers.py	71.11% <100.00%> (-0.32%)	:arrow_down:
ord_schema/scripts/process_dataset.py	79.28% <100.00%> (+0.30%)	:arrow_up:
ord_schema/scripts/validate_dataset.py	90.00% <100.00%> (ø)
ord_schema/templating.py	94.91% <100.00%> (+0.08%)	:arrow_up:
ord_schema/units.py	86.41% <100.00%> (ø)
ord_schema/updates.py	95.34% <100.00%> (-0.11%)	:arrow_down:
... and 3 more

[ord-service]

LGTM. There's some guidance at Google about how you ought to use various incantations of Iterable or AbstractX to annotate args/return values, but I think the list stuff is probably the right choice for simplicity

Thanks; that guidance is in the typing docs as well. Updated most of the args to match.