build: Add `error_set` and audit `unicode-ident` #1

Job	Run time
Quality Control	19s
Build & Test (macos-latest) (Nightly)	22s
Build & Test (windows-latest) (Nightly)	36s
Build & Test (ubuntu-latest) (Nightly)	20s
Build & Test (macos-latest) (MSRV)	20s
Build & Test (ubuntu-latest) (MSRV)	20s
Build & Test (windows-latest) (MSRV)	42s
	2m 59s

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