refactor: Remove slot mutex and simplify per blob state #454

Job	Run time
Cross Build Only (x86_64-unknown-freebsd)	50s
Cross Test (i686-unknown-linux-gnu)	1m 45s
Android Build Only (armv7-linux-androideabi)	1m 9s
Android Build Only (aarch64-linux-android)	1m 8s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	3m 34s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	2m 2s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	43s
clippy_check	1m 55s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1m 40s
Minimal Supported Rust Version	1m 14s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	1m 40s
codespell	6s
check_semver	1m 12s
cargo deny	30s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 23s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1m 37s
Checking fmt	29s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 31s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 39s
Checking docs	1m 4s
	27m 11s

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