refactor: change `SCCNonlinearProblem` fields #536

Job	Run time
Tests (1, Core) / Tests - Core	4m 26s
Tests (1, Downstream) / Tests - Downstream	31m 46s
Tests (1, Python) / Tests - Python	7m 42s
Tests (1, QA) / Tests - QA	4m 11s
Tests (lts, Core) / Tests - Core	6m 18s
Tests (lts, Downstream) / Tests - Downstream	25m 58s
Tests (lts, Python) / Tests - Python	7m 1s
Tests (pre, Core) / Tests - Core	4m 31s
Tests (lts, QA) / Tests - QA	3m 47s
Tests (pre, Downstream) / Tests - Downstream	31m 43s
Tests (pre, Python) / Tests - Python	7m 39s
Tests (pre, QA) / Tests - QA	1m 20s
	2h 16m 22s

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