Added unit tests for `PMatrix3D` in `processing:core` #133

Job	Run time
Test Processing	1m 20s
(linux/aarch64) Create Processing Build	8m 36s
(linux/x64) Create Processing Build	8m 50s
(windows/x64) Create Processing Build	7m 35s
(macos/x64) Create Processing Build	5m 24s
(macos/aarch64) Create Processing Build	3m 40s
	35m 25s

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