fix: lake: pin mathlib in `new`/`init` to toolchain #45821

Job	Run time
configure	7s
build / Linux Lake	10m 36s
build-secondary / Linux release	38m 32s
build-secondary / macOS aarch64	38m 36s
Build matrix complete	3s
release	0s
release-nightly	0s
	1h 27m 54s

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