Improve the type annotation completedness

[mwouts]

ITables v2.4.1 will have py.typed markers. But the type annotations can still be improved. As diagnosed with

pyright --ignoreexternal --verifytypes  itables 

on https://github.com/mwouts/itables/pull/389, the type completedness is 69.9%:

Symbols exported by "itables": 209
  With known type: 146
  With ambiguous type: 2
  With unknown type: 61
    (Ignoring unknown types imported from other packages)

Other symbols referenced but not exported by "itables": 6
  With known type: 0
  With ambiguous type: 2
  With unknown type: 4

Symbols without documentation:
  Functions without docstring: 18
  Functions without default param: 0
  Classes without docstring: 1

Type completeness score: 69.9%

Completed in 1.988sec

(and it's only 25% for itables_for_dash)