Add type hints

[adamjstewart]

No description provided.

[codecov-commenter]

Codecov Report

Merging #28 (84b9607) into main (07b7e04) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 84b9607 differs from pull request most recent head f613b61. Consider uploading reports for the commit f613b61 to get more accurate results

@@            Coverage Diff             @@
##              main       #28    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files            1         2     +1     
  Lines          534      1137   +603     
==========================================
+ Hits           534      1137   +603     

Impacted Files	Coverage Δ
fiscalyear.py	100.00% <100.00%> (ø)
test_fiscalyear.py	100.00% <100.00%> (ø)

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