v0.2.1: hardening + perf + DX + operational maturity #27

Job	Run time
test (ubuntu-latest)	44s
cargo-audit (security advisories)	2m 59s
test (windows-latest)	2m 25s
msrv (rust 1.83)	13s
criterion benches (compile only)	2m 23s
coverage (llvm-cov)	1m 10s
test (macos-latest)	41s
	10m 35s

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