Fix offchain election to respect the weight (#7215)

* Mockup

* Fix offchain election to respect the weight

* Fix builds a bit

* Update frame/staking/src/offchain_election.rs

Co-authored-by: Shawn Tabrizi <[email protected]>

* Update frame/staking/src/offchain_election.rs

Co-authored-by: Shawn Tabrizi <[email protected]>

* Make it build, binary search

* Fix a number of grumbles

* one more fix.

* remove unwrap.

* better alg.

* Better alg again.

* Final fixes

* Fix

* Rollback to normal

* Final touches.

* Better tests.

* Update frame/staking/src/lib.rs

Co-authored-by: Guillaume Thiolliere <[email protected]>

* Proper maxExtWeight

* Final fix

* Final fix for the find_voter

Co-authored-by: Shawn Tabrizi <[email protected]>
Co-authored-by: Guillaume Thiolliere <[email protected]>