Tests

Implement `lastindex` for ragged arrays #263

Job	Run time
Tests (lts, Core) / Tests - Core	3m 45s
Tests (pre, Core) / Tests - Core	3m 40s
Tests (1, Downstream) / Tests - Downstream	16m 54s
Tests (1, Core) / Tests - Core	4m 40s
Tests (pre, Downstream) / Tests - Downstream	18m 46s
Tests (lts, Downstream) / Tests - Downstream	10m 10s
	57m 55s

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