Remove intermediate allocations for error messages #1010

Job	Run time
Rustfmt	13s
Book	2s
Check order in Cargo.toml	3s
Audit	17s
DevSkim	33s
Docs (rinja)	22s
Jinja2-Assumptions	19s
Docs (rinja_derive)	21s
Typos	25s
Docs (rinja_parser)	20s
MSRV	19s
Test (ubuntu-latest, stable)	57s
Test (ubuntu-latest, beta)	45s
Package (examples/actix-web-app)	50s
Test (macos-latest, stable)	58s
Package (examples/axum-app)	33s
Package (examples/poem-app)	45s
Test (windows-latest, stable)	1m 58s
Package (examples/rocket-app)	1m 9s
Package (examples/salvo-app)	1m 3s
Package (examples/warp-app)	1m 3s
Package (fuzzing)	28s
Package (rinja)	41s
Package (rinja_derive)	15s
Package (rinja_derive_standalone)	36s
Package (rinja_parser)	40s
Package (testing)	1m 7s
Package (testing-alloc)	20s
Package (testing-no-std)	14s
Cluster-Fuzz	14m 3s
Fuzz (all)	5m 19s
Fuzz (filters)	5m 17s
Fuzz (html)	5m 12s
Fuzz (parser)	5m 15s
	52m 42s

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