* Dissolve legacy `sync/types.nim` into `*/eth/eth_types.nim`
* Flare sync: Simplify scheduler and remove `runSingle()` method
why:
`runSingle()` is not used anymore (main purpose was for negotiating
best headers in legacy full sync.)
Also, `runMulti()` was renamed `runPeer()`
* Flare sync: Move `chain` field from `sync_desc` -> `worker_desc`
* Flare sync: Remove handler descriptor lateral reference
why:
Not used anymore. It enabled to turn on/off eth handler activity with
regards to the sync state, i.e.from with in the sync worker.
* Flare sync: Update `Hash256` and other deprecated `std/eth` symbols
* Protocols: Update `Hash256` and other deprecated `std/eth` symbols
* Eth handler: Update `Hash256` and other deprecated `std/eth` symbols
* Update flare TODO
* Remove redundant `sync/type` import
why:
The import module `type` has been removed
* Remove duplicate implementation
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