[hackathon] feat: add HostNotifier trait and decouple node from ExExContext #466

Job	Run time
rust-library-base / Feature Checks	4m 40s
rust-library-base / Base Checks / Test Suite	7m 51s
rust-library-base / Base Checks / doctest	5m 26s
rust-library-base / Base Checks / Clippy	4m 21s
rust-library-base / Base Checks / Rustfmt	39s
rust-library-base / Base Checks / Docs	4m 11s
	27m 8s

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