Improve types and undo #240

[hoangvvo]

This allows calling applySession, withSession, and session with a generic that represents the shape of req.session.

Also undo #240 become it is quite problematic. (user wants to committed but then mutate and committed again)

[codecov]

Codecov Report

Merging #252 into master will decrease coverage by 0.77%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #252      +/-   ##
==========================================
- Coverage   95.34%   94.57%   -0.78%     
==========================================
  Files           9        9              
  Lines         172      166       -6     
  Branches       46       50       +4     
==========================================
- Hits          164      157       -7     
  Misses          2        2              
- Partials        6        7       +1     

Impacted Files	Coverage Δ
src/types.ts	100.00% <ø> (ø)
src/connect.ts	100.00% <100.00%> (ø)
src/core.ts	93.33% <100.00%> (-3.22%)	⬇️
src/session.ts	90.00% <100.00%> (-1.90%)	⬇️
src/withSession.ts	83.33% <100.00%> (ø)

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