* Log/trace cancellation events in scheduler
* Provide `clear()` functions for explicitly flushing data objects
* Renaming header cache functions
why:
More systematic, all functions start with prefix `dbHeader`
* Remove `danglingParent` from layout
why:
Already provided by header cache
* Remove `couplerHash` and `headHash` from layout
why:
No need to cache, `headHash` is unused and `couplerHash` used typically
once, only.
* Remove `lastLayout` from sync descriptor
why:
No need to compare changes, saving is always triggered after actively
changing the sync layout state
* Early reject unsuitable head + finalised header from CL
why:
The finalised header is only passed by its hash so the header must be
fetched somewhere, e.g. from a peer via eth/xx.
Also, finalised headers earlier than the `base` from `FC` cannot be
handled due to the `Aristo` single state database architecture.
Luckily, on a full node, the complete block history is available so
unsuitable finalised headers are stored there already which is exploited
here to avoid unnecessary network traffic.
* Code cosmetics, remove cruft, prettify logging, remove `final` metrics
detail:
The `final` layout parameter will be deprecated and later removed
* Update/re-calibrate syncer logic documentation
why:
The current implementation sucks if the `FC` module changes the
canonical branch in the middle of completing a header chain (due
to concurrent updates by the `newPayload()` logic.)
* Implement according to re-calibrated syncer docu
details:
The implementation employs the notion of named layout states (see
`SyncLayoutState` in `worker_desc.nim`) which are derived from the
state parameter triple `(C,D,H)` as described in `README.md`.
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