* feat(op-service):add open_db_read_only func, return reth db instance to go

* feat(op-service):store reth db instance in go,

* fix fmt

* feat(op-service):check err when create RethFetcher

* feat(op-service):add func comments
Co-authored-by: Joshua Gutow <jbgutow@gmail.com>

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Co-authored-by: Joshua Gutow <jbgutow@gmail.com>