allow try-runtime and `TestExternalities` to report PoV size (#10372)

* allow try-runtime and test-externalities to report proof size

* self review

* fix test

* Fix humanized dispaly of bytes

* Fix some test

* Fix some review grumbles

* last of the review comments

* fmt

* remove unused import

* move test

* fix import

* Update primitives/state-machine/src/testing.rs

Co-authored-by: Bastian Köcher <[email protected]>

* last touches

* fix

Co-authored-by: Bastian Köcher <[email protected]>