[guppy] update to cargo_metadata 0.19.1, replace manual to_string impls #1275

Job	Run time
Build and test (all features) (ubuntu-latest, 1.75)	11s
Build and test core crates (ubuntu-latest, 1.75)	39s
Build documentation (ubuntu-latest)	1m 1s
Cross-compile to aarch64	1m 38s
Build and test (all features) (ubuntu-latest, stable)	39s
Build and test core crates (ubuntu-latest, stable)	44s
Build and test (all features) (macos-14, 1.75)	24s
Build and test core crates (macos-14, 1.75)	36s
Lint	30s
cargo-compare extended tests (ubuntu-latest)	23s
Build and test (all features) (macos-14, stable)	34s
Build and test core crates (macos-14, stable)	35s
cargo-compare extended tests (macos-14)	30s
Build and test (all features) (windows-latest, 1.75)	1m 58s
Build and test core crates (windows-latest, 1.75)	1m 19s
Build and test (all features) (windows-latest, stable)	1m 51s
Build and test core crates (windows-latest, stable)	1m 35s
	15m 7s

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