`stake-tracker` feedback PR (#4411)

- Changes the target list score type from balance to `u128`
(`ExtendedBalance`)
  - simplifies `balance/ vote_weight/ extended_balance` conversions
  - relies less on the currency total issuance call
  - ensures approval stake calculations/storage is safe 
- Simplifies stake tracker logic
  - removes a few redundant checks
  - split `on_stake_update` code
- Ensures `VoterUpdateMode` is taken into consideration in try-state
checks
  - use voter mode lazy in benchmarks
  - update weights + check the diff with voter lazy 
- Docs improvements
- All tests passing after merging validator disabling and virtual
stakers

**new**
- ensures duplicate nominations are dedup before calculating the
approvals stake
- chills nominator after total slash to ensure the target can be
reaped/kill without leaving nominations behind.
- ensures that switching from validator to nominator and back is correct
- a nominator may have an entry in the targetlist (if it was a validator
+ has nominations)
  - ensure target node is removed if balance is 0 and it is a nominator.
- addresses
https://github.com/paritytech-secops/srlabs_findings/issues/383

---
**Other experiments:** (not included)
- https://github.com/paritytech/polkadot-sdk/pull/4402 (passing the
status of the staker with who in the OnStakingUpdate interface is less
clean, it turns out)
- https://github.com/paritytech/polkadot-sdk/pull/4361

---------

Co-authored-by: command-bot <>