Read placeholders from `cargo-generate.toml` #27

Job	Run time
xtask test & lint	2m 1s
test (ubuntu-24.04, spirv-builder)	5m 36s
test (ubuntu-24.04, cargo-gpu)	7m 28s
test (macOS-latest, spirv-builder)	7m 53s
test (windows-2022, spirv-builder)	8m 45s
test (macOS-latest, cargo-gpu)	10m 9s
lint (spirv-builder)	5m 23s
test (windows-2022, cargo-gpu)	12m 7s
lint (cargo-gpu)	6m 54s
test_success	2s
	1h 6m 18s

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