Introduce HasSpan trait #66

Job	Run time
Enforce Rust code format	13s
Clippy	15s
License / vulnerability audit (advisories)	15s
Preflight docs.rs build	15s
License / vulnerability audit (bans licenses sources)	17s
Preflight crate publish (ubuntu-latest, stable)	19s
Unit tests with minimum versions of direct dependencies (windows-latest)	41s
Unit tests (windows-latest, stable)	1m 2s
Check for unused dependencies	19s
Unit tests with minimum versions of direct dependencies (macos-latest)	31s
Unit tests (windows-latest, 1.72.0)	39s
Unit tests with minimum versions of direct dependencies (ubuntu-latest)	18s
Unit tests (macos-latest, stable)	2m 18s
Unit tests (macos-latest, 1.72.0)	37s
Unit tests (ubuntu-latest, stable)	20s
Unit tests (ubuntu-latest, 1.72.0)	25s
	8m 44s

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