slots: incrementally backoff claiming slots if finality lags behind (#7186)

* babe: backoff authoring blocks when finality lags

* babe: move backoff authoring params to default constructor

* babe: deduplicate the test a bit

* babe: set backoff constants in service

* babe: use better names for backoff authoring block parameters

* babe: remove last unwrap

* babe: slight style tweak

* babe: fix comment

* slots: move backoff block authorship logic to SimpleSlotWorker

* aura: append SlotInfo in on_slot

* slots: use the correct types for parameters

* slots: fix review comments

* aura: add missing backoff authoring blocks parameters

* slots: add comments for default values

* slots: add additional checks in test

* slots: update implementation for new master

* slots: revert the change to SlotInfo

* Fix review comments

* slots: rework unit tests for backing off claiming slots

* slots: add test for asymptotic behaviour for slot claims

* slots: address review comments

* slots: add test for max_interval

* slots: add assertion for intervals between between claimed slots

* slots: remove rustfmt directive

* slots: another attempt at explaining authoring_rate

* slots: up unfinalized_slack to 50 by default

* slots: add tests for time to reach max_interval

* slots: fix typo in comments

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* slots: additional tweaks to comments and info calls

* slots: rename to BackoffAuthoringOnFinalizedHeadLagging

* slots: make the backing off strategy generic

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* slots: implement backoff trait for () for simplicity

* slots: move logging inside backing off function to make it more specific

* aura: add missing function parameter

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>