feat(cesium): implement tileset.rs cold-import parser — Group-A entry, no-serde #515

Job	Run time
native-backend/stable	8m 18s
hpc-stream-parallel/rayon	1m 26s
nostd/thumbv6m-none-eabi/stable	29s
Pass MSRV values to other jobs	2s
format/stable	21s
tier4-avx512-check	30s
clippy/1.95.0	41s
cargo-careful	0s
nightly-simd-polyfill	0s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	0s
miri	0s
docs/nightly	0s
tests/beta	11m 9s
blas-msrv	48s
tests/1.95.0	10m 49s
tests/stable	10m 26s
conclusion	-1s
	44m 58s

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