feat: JournalDb trait #90

Job	Run time
rust-library-base / Base Checks / doctest	2m 18s
rust-library-base / Feature Checks	44s
rust-library-base / Base Checks / Test Suite	1m 39s
rust-library-base / Base Checks / Rustfmt	21s
rust-library-base / Base Checks / Docs	1m 34s
rust-library-base / Base Checks / Clippy	1m 45s
	8m 21s

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