Merge pull request #588 from SpiNNakerManchester/remove_vertex_union #1901

Job	Run time
call / validate (ubuntu-latest, 3.12, validate)	5m 39s
call / checks (ubuntu-latest, 3.13)	1m 55s
call / tests (windows-latest, 3.12, tests)	1m 56s
call / checks (ubuntu-24.04, 3.11)	1m 41s
call / tests (windows-2019, 3.9, tests)	2m 33s
call / checks (ubuntu-latest, 3.10)	2m 10s
call / tests (macos-latest, 3.13, tests)	1m 16s
call / checks (ubuntu-22.04, 3.9)	2m 9s
call / tests (macos-13, 3.9, tests)	2m 57s
call / checks (ubuntu-20.04, 3.8)	2m 9s
	24m 25s

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