* allow trusted node sync based on LC trusted block root
Extends `trustedNodeSync` with a new `--trusted-block-root` option that
allows initializing a light client. No `--state-id` must be provided.
The beacon node will then use this light client to obtain the latest
finalized state from the remote server in a trust-minimized fashion.
Note that the provided `--trusted-block-root` should be somewhat recent,
and that security precautions such as comparing the state root against
block explorers is still recommended.
* fix
* workaround for `valueOr` limitations
* reduce magic numbers
* digest len > context len for readability
* move `cstring` conversion to caller
* avoid abbreviations
* `return` codestyle