Replace `from_utf8_unsafe()` with `AsciiStr` #1089

Job	Run time
Audit	20s
Book	6s
DevSkim	30s
Check order in Cargo.toml	3s
Docs (rinja)	22s
Rustfmt	18s
Docs (rinja_derive)	24s
Jinja2-Assumptions	11s
Typos	22s
Docs (rinja_parser)	17s
MSRV	20s
Test (ubuntu-latest, stable)	52s
Test (ubuntu-latest, beta)	40s
Test (macos-latest, stable)	58s
Package (bench-build)	21s
Test (windows-latest, stable)	2m 11s
Package (examples/actix-web-app)	59s
Package (examples/axum-app)	45s
Package (examples/poem-app)	49s
Package (examples/rocket-app)	1m 25s
Package (examples/salvo-app)	1m 11s
Package (examples/warp-app)	1m 4s
Package (fuzzing)	57s
Package (rinja)	39s
Package (rinja_derive)	34s
Package (rinja_derive_standalone)	42s
Package (rinja_parser)	43s
Package (testing)	1m 12s
Package (testing-alloc)	22s
Package (testing-no-std)	22s
Package (testing-renamed)	23s
Cluster-Fuzz	14m 9s
Fuzz (all)	5m 21s
Fuzz (filters)	5m 30s
Fuzz (html)	5m 18s
Fuzz (parser)	5m 14s
	55m 54s

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