Read placeholders from `cargo-generate.toml` #30

Job	Run time
xtask test & lint	1m 41s
test (ubuntu-24.04, cargo-gpu)	3m 25s
test (windows-2022, cargo-gpu)	3m 20s
lint (spirv-builder)	3m 25s
test (windows-2022, spirv-builder)	3m 21s
test (ubuntu-24.04, spirv-builder)	3m 24s
lint (cargo-gpu)	3m 24s
test (macOS-latest, spirv-builder)	3m 30s
test (macOS-latest, cargo-gpu)	3m 27s
test_success	4s
	29m 1s

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