Finish async signing implementation for cose_sign #1712

Job	Run time
Clippy	30s
Preflight docs.rs build	1m 50s
Enforce Rust code format	15s
License / vulnerability audit (advisories)	24s
Preflight crate publish (ubuntu-latest, stable)	53s
License / vulnerability audit (bans licenses sources)	26s
Unit tests with minimum versions of direct dependencies (windows-latest)	2m 15s
Unit tests (aarch64-unknown-linux-gnu, stable)	3m 28s
Unit tests with minimum versions of direct dependencies (macos-latest)	2m 15s
Unit tests (WASM)	1m 5s
Unit tests (windows-latest, stable)	11m 27s
Unit tests (aarch64-unknown-linux-gnu, 1.70.0)	4m 6s
Unit tests with minimum versions of direct dependencies (ubuntu-latest)	1m 7s
Unit tests (windows-latest, 1.70.0)	11m 14s
Check for unused dependencies	2m 18s
Unit tests (macos-latest, stable)	9m 56s
Ensure (MINOR) tag is used when making an API breaking change	2m 10s
Unit tests (macos-latest, 1.70.0)	11m 55s
Unit tests (ubuntu-latest, stable)	2m 6s
Unit tests (ubuntu-latest, 1.70.0)	1m 21s
	1h 11m 1s

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