Tests

Achieve type stability for indexing by avoiding variable boxing, including for ranges #326

Job	Run time
Tests (1, Core) / Tests - Core	6m 11s
Tests (1, nopre) / Tests - nopre	7m 21s
Tests (lts, Core) / Tests - Core	9m 38s
Tests (lts, nopre) / Tests - nopre	2m 43s
Tests (pre, Downstream) / Tests - Downstream	23m 39s
Tests (1, Downstream) / Tests - Downstream	12m 54s
Tests (lts, Downstream) / Tests - Downstream	9m 3s
Tests (pre, Core) / Tests - Core	5m 18s
	1h 16m 47s

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