feat(x86_64): real abstraction for ISA IRQs, unfuck I/O APIC #1406

Job	Run time
changed_paths	8s
cargo check (host)	3m 38s
clippy	2m 47s
build boot image (x86_64)	3m 8s
rustfmt	14s
cargo test (host)	4m 41s
Loom tests (cordyceps)	1m 43s
Miri tests (cordyceps)	1m 57s
docs	4m 17s
Loom tests (maitake)	4m 11s
Miri tests (maitake)	18m 5s
Tests (maitake, no-default-features)	1m 41s
cargo test (cross x64)	4m 43s
all_systems_go	1s
	51m 14s

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