staking: avoid proportional slashing leak dust into chunks that should not be slashed (#12058)

* replace slash ratio with remaining ratio

Signed-off-by: linning <linningde25@gmail.com>

* little refactor

Signed-off-by: linning <linningde25@gmail.com>

* fix test

Signed-off-by: linning <linningde25@gmail.com>

* fix typo

Signed-off-by: linning <linningde25@gmail.com>

* revert refactor

Signed-off-by: linning <linningde25@gmail.com>

* rounding up instead of remaining ratio

Signed-off-by: linning <linningde25@gmail.com>

* address comment

Signed-off-by: linning <linningde25@gmail.com>

* Update frame/nomination-pools/test-staking/src/lib.rs

Signed-off-by: linning <linningde25@gmail.com>

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update frame/nomination-pools/test-staking/src/lib.rs

Signed-off-by: linning <linningde25@gmail.com>

Co-authored-by: Roman Useinov <roman.useinov@gmail.com>

Signed-off-by: linning <linningde25@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Roman Useinov <roman.useinov@gmail.com>
Co-authored-by: parity-processbot <>