Read placeholders from `cargo-generate.toml` #31

Job	Run time
xtask test & lint	1m 54s
lint (cargo-gpu)	6m 47s
test (windows-2022, cargo-gpu)	12m 4s
test (ubuntu-24.04, cargo-gpu)	7m 59s
lint (spirv-builder)	5m 42s
test (windows-2022, spirv-builder)	9m 19s
test (macOS-latest, cargo-gpu)	10m 44s
test (macOS-latest, spirv-builder)	9m 43s
test (ubuntu-24.04, spirv-builder)	5m 54s
test_success	4s
	1h 10m 10s

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