fix(genesis): Add `osakaTime` to `mainnet.genesis.json` #249

Job	Run time
rust-library-base / Feature Checks	1m 27s
rust-library-base / Base Checks / Test Suite	4m 34s
rust-library-base / Base Checks / doctest	1m 28s
rust-library-base / Base Checks / Clippy	1m 10s
rust-library-base / Base Checks / Docs	20s
rust-library-base / Base Checks / Rustfmt	16s
	9m 15s

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