Remove const_cast from MuonSegmentRegionRecoveryTool

MuonSegmentRegionRecoveryTool was unnecessarily treating the tracks it creates as const, even though they are not. Removing the unnecessary consts means that the const_casts can be removed as well. I took advantage of the changes to move to unique_ptr for the parts of the code affected by them. Partially resolves ATLASRECTS-5250.