feat: add caching to GapicCallable (#666)

* feat: optimize _GapicCallable

* cleaned up metadata lines

* chore: avoid type checks in error wrapper

* Revert "chore: avoid type checks in error wrapper"

This reverts commit c97a6365028f3f04d20f26aa1cc0e3131164f53e.

* add default wrapped function

* fixed decorator order

* fixed spacing

* fixed comment typo

* fixed spacing

* fixed spacing

* removed unneeded helpers

* use caching

* improved metadata parsing

* improved docstring

* fixed logic

* added benchmark test

* update threshold

* run benchmark in loop for testing

* use verbose logs

* Revert testing

* used smaller value

* changed threshold

* removed link in comment

* use list type for metadata

* add types to docstring

* fixed lint

* convert to list at init time

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Co-authored-by: Daniel Sanche <sanche@google.com>
Co-authored-by: Daniel Sanche <d.sanche14@gmail.com>