Add tests for Polkadot runtime weights and fees (#1090)

* Add tests for Balance module weights

* Add tests for some of the Staking functions

* Add tests for system Pallet weights

* Add weight tests for Session pallet

* Add tests for Democracy Pallet weights

* Add tests for Phragment weights

* Add tests for Treasury weights

* Use consistent naming for tests

* Split tests into separate weight and fee suites

* Move weight constant checks into one test

* Use formulas instead of hardcoded weights

* Slim down number of tests

Mainly removing ones that are either root calls that aren't "important",
or others which will likely change if another test (which we kept) also
changes.

* Update timestamp set() weight

* Update Staking Pallet weights

* Update Democracy Pallet weights

* Update copyright year

Co-authored-by: Kian Paimani <[email protected]>

Co-authored-by: Kian Paimani <[email protected]>