feat(x86_64): real abstraction for ISA IRQs, unfuck I/O APIC #1403

Job	Run time
changed_paths	6s
cargo test (host)	4m 37s
clippy	2m 56s
cargo check (host)	3m 35s
rustfmt	15s
build boot image (x86_64)	3m 18s
Loom tests (cordyceps)	1m 24s
Miri tests (cordyceps)	2m 10s
docs	2m 2s
Loom tests (maitake)	4m 10s
Miri tests (maitake)	18m 50s
Tests (maitake, no-default-features)	1m 44s
cargo test (cross x64)	4m 36s
Loom tests (mycelium-util)	53s
all_systems_go	0s
	50m 36s

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