Use strict types

[dbartholomae]

Closes #36

Checklist:

• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.

[codecov]

Codecov Report

Merging #38 into main will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #38   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           53        54    +1     
  Lines          519       520    +1     
  Branches        98        98           
=========================================
+ Hits           519       520    +1     

Impacted Files	Coverage Δ
packages/compose/src/compose.ts	100.00% <ø> (ø)
packages/compose/src/compose-handler.ts	100.00% <100.00%> (ø)
...tp-header-normalizer/src/http-header-normalizer.ts	100.00% <100.00%> (ø)
...ddy-adaptor/src/MiddyMiddleware/MiddyMiddleware.ts	100.00% <100.00%> (ø)
...or/src/MiddyMiddleware/promisifyMiddyMiddleware.ts	100.00% <100.00%> (ø)
...iddyMiddleware/promisifyMiddyMiddlewareFunction.ts	100.00% <100.00%> (ø)
packages/middy-adaptor/src/middy-adaptor.ts	100.00% <100.00%> (ø)
packages/utils/src/promisifyHandler.ts	100.00% <100.00%> (ø)

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