* Fix name after API change
why:
Slipped through (debugging mode)
* Fine tuning error counters
why:
Previous operating mode was quite blunt and considered some unnecessary
condition. Error handling was invoked and the peer zombified where one
could have continued working with that peer.
* Provide `kvt` table API bypassing `FC`
details:
Not a full bypass yet
why:
As discussed on Discord:
Ideally, those would pass through fc as well, as thin wrappers around
the db calls, for now - later, we probably see some policy involved
here and at that point, fc will be responsible for arbitrage between
sources (ie if a rpc source sends the block the syncer is syncing
while the syncer is working, fc is there to referee

* Apply `kvt` API from `FC` to beacon sync
* No need to use extra table for persistent header cache state record
why:
Slot zero can do. This allows deleting that table wholesale when needed
once thatfeature is available.
* Logger updates
details:
+ Lifting main header/block op logs from `trace` to `debug`
+ Set metrics update before nano-sleep (for task switch)
* Re-org internal descriptor `CanonicalDesc` as `PivotArc`
why:
Despite its name, `CanonicalDesc` contained a cursor arc (or leg) from
the base tree with a designated block (or Header) on its arc members
(aka blocks.) The type is used more generally than only for s block on
the canonical cursor.
Also, the `PivotArc` provides some more fields for caching intermediate
data. This simplifies managing extra arguments for some functions.
* Remove cruft
details:
No need to find cursor arc if it is given as function argument.
* Rename prototype variables `head: PivotArc` to `pvarc`
why:
Better reading
* Function and code massage, adjust names
details:
Avoid the syllable `canonical` in function names that do not strictly
apply to the canonical chain. So renaming
* findCanonicalHead() => findCursorArc()
* canonicalChain() => findHeader()
* trimCanonicalChain() => trimCursorArc()
* Combine `updateBase()` function-args into single `PivotArgs` object
why:
Will generalise action for more complex scenarios in future.
* update `calculateNewBase()` return code type => `PivotArc`
why:
So it can directly be used as argument into `updateBase()`
* Update `calculateNewBase()` for target on parent arc
* Update unit tests
* Kludge: fix `eip4844` import in `validate`
why:
Importing `validate` needs `blscurve` here or with the importing module.
* Separate out `FC` descriptor iinto separate file
why:
Needed for external descriptor access (e.g. for debugging)
* Debugging toolkit for `FC`
* Verify chain descriptor after changing state
Jordan Hrycaj