Add UnitConversion guide v4 #1881

Job	Run time
cache-pixi-lock / Generate output	11s
TypeChecking: pixi run typing	0s
Unit tests: ubuntu \| pixi run -e test-py313 tests	3m 28s
Unit tests: ubuntu \| pixi run -e test-latest tests	3m 36s
Unit tests: ubuntu \| pixi run -e test-minimum tests	3m 39s
Unit tests: windows \| pixi run -e test-latest tests	8m 56s
Unit tests: ubuntu \| pixi run -e test-py311 tests	3m 45s
Integration: ${{ matrix.os }} \| pixi run -e ${{ matrix.pixi-environment }} tests-notebooks	-1s
merge-test-artifacts	-1s
	23m 33s

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