Upstream newSeqUninitialized instantiation issue.
The `newSeqUninitialized` proc added in January should be a drop-in replacement for `newSeqUninit` but as showed by CI in commit https://github.com/mratsim/Arraymancer/commit/b306dd8e76d807ce897dbfc837801b5624e2f546 Nim has trouble instantiating the generic type.

For now commit https://github.com/mratsim/Arraymancer/commit/50f7c316d696a20479c4f5e17759b45c2bd90bf4 reverted the change.