fix(genesis): Add `osakaTime` to `mainnet.genesis.json` #250

Job	Run time
rust-library-base / Feature Checks	1m 6s
rust-library-base / Base Checks / Rustfmt	22s
rust-library-base / Base Checks / Clippy	1m 5s
rust-library-base / Base Checks / doctest	1m 14s
rust-library-base / Base Checks / Docs	21s
rust-library-base / Base Checks / Test Suite	3m 22s
	7m 30s

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