Add support for generics syntax in parser #994

Job	Run time
Book	3s
Audit	17s
Check order in Cargo.toml	4s
DevSkim	29s
Docs (rinja)	21s
Jinja2-Assumptions	16s
Docs (rinja_derive)	20s
Rustfmt	14s
Docs (rinja_parser)	19s
Typos	24s
MSRV	20s
Test (ubuntu-latest, stable)	57s
Test (ubuntu-latest, beta)	46s
Package (examples/actix-web-app)	1m 2s
Test (macos-latest, stable)	43s
Package (examples/axum-app)	45s
Test (windows-latest, stable)	2m 29s
Package (examples/poem-app)	54s
Package (examples/rocket-app)	1m 23s
Package (examples/salvo-app)	1m 10s
Package (examples/warp-app)	1m 0s
Package (fuzzing)	33s
Package (rinja)	43s
Package (rinja_derive)	28s
Package (rinja_derive_standalone)	44s
Package (rinja_parser)	37s
Package (testing)	1m 7s
Package (testing-alloc)	23s
Package (testing-no-std)	23s
Cluster-Fuzz	14m 19s
Fuzz (all)	5m 12s
Fuzz (filters)	5m 18s
Fuzz (html)	5m 9s
Fuzz (parser)	5m 19s
	54m 31s

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