Revert Cargo.toml union-merge driver — it mangles [[example]] blocks #618

Job	Run time
hpc-stream-parallel/rayon	1m 27s
format/stable	20s
tier4-avx512-check	40s
native-backend/stable	8m 14s
Pass MSRV values to other jobs	3s
nostd/thumbv6m-none-eabi/stable	33s
clippy/1.95.0	40s
cargo-careful	0s
miri	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
nightly-simd-polyfill	0s
docs/nightly	-8s
tests/stable	11m 10s
tests/beta	11m 12s
tests/1.95.0	11m 26s
blas-msrv	59s
conclusion	0s
	46m 36s

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