feat: remove `Rc<RefCell<Context>>` from `hp::Key` #110

Job	Run time
Determine toolchains	5s
cargo clippy (ubuntu-24.04, stable)	2m 50s
cargo clippy (macos-15, nightly)	6m 22s
cargo clippy (windows-2025, 1.90.0)	5m 30s
cargo clippy (macos-15, stable)	3m 29s
cargo clippy (windows-2025, stable)	7m 8s
cargo clippy (windows-2025, nightly)	9m 34s
cargo clippy (macos-15, 1.90.0)	1m 27s
cargo clippy (ubuntu-24.04, 1.90.0)	1m 21s
cargo clippy (ubuntu-24.04, nightly)	3m 8s
	40m 54s

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