triedb/pathdb: support v0 journal format (ethereum-optimism#368)

* triedb/pathdb: support v0 journal format

* Update triedb/pathdb/journal.go - use %w in Errorf

* triedb/pathdb: add warn log when loading legacy v0 journal

* triedb/pathdb: flatten journal.go code

Co-authored-by: Sebastian Stammler <[email protected]>

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Co-authored-by: Sebastian Stammler <[email protected]>