Manual Seal (#4143)

* instant/manual seal

unbounded queues are evil

Apply suggestions from code review

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

add fork tests, docs, remove todos

moar docs

Update client/consensus/manual-seal/src/rpc.rs

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

remove unbound generic, parameter, docs, deps, code style changes

Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

code style chnges

remove unused deps, remove dep renames, check if block is empty before importing, use ? for error propagation

fix tests

log errors for instant seal

use debug

code style changes, updated copyright dates

use txpool::Pool instead of BasicPool, code style changes

fixed tests

* fix tests

* requested changes from review

* check inherents len

* rebase