Read placeholders from `cargo-generate.toml` #32

Job	Run time
lint (spirv-builder)	5m 20s
lint (cargo-gpu)	7m 16s
xtask test & lint	2m 4s
test (windows-2022, cargo-gpu)	11m 20s
test (macOS-latest, cargo-gpu)	7m 7s
test (ubuntu-24.04, spirv-builder)	5m 55s
test (ubuntu-24.04, cargo-gpu)	7m 51s
test (macOS-latest, spirv-builder)	7m 19s
test (windows-2022, spirv-builder)	9m 27s
test_success	2s
	1h 3m 41s

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