feat(x86_64): real abstraction for ISA IRQs, unfuck I/O APIC #1399

Job	Run time
changed_paths	5s
cargo test (host)	4m 46s
cargo check (host)	3m 49s
clippy	2m 52s
rustfmt	16s
build boot image (x86_64)	3m 24s
Loom tests (cordyceps)	1m 45s
Miri tests (cordyceps)	2m 8s
docs	2m 10s
Loom tests (maitake)	4m 14s
Miri tests (maitake)	18m 36s
Tests (maitake, no-default-features)	1m 44s
cargo test (cross x64)	4m 27s
Loom tests (mycelium-util)	1m 4s
all_systems_go	0s
	51m 20s

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