a few misc tweaks

[samuelcolvin]

• clean up two bits of code
• revert Cargo.toml to double quotes
• switch actions-rs/toolchain -> dtolnay/rust-toolchain
• cleanup ci.yml

[codecov-commenter]

Codecov Report

Merging #315 (f33147b) into main (bcf799f) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
- Coverage   97.36%   97.36%   -0.01%     
==========================================
  Files          55       55              
  Lines        6346     6334      -12     
  Branches       44       44              
==========================================
- Hits         6179     6167      -12     
  Misses        167      167              

Impacted Files	Coverage Δ
src/input/input_python.rs	98.19% <100.00%> (ø)
src/validators/typed_dict.rs	99.05% <100.00%> (-0.04%)	⬇️

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