STYLE: use unique_ptr for Fstream resource management

src/OpenFOAM/db/IOstreams/Fstreams/IFstream.C

src/OpenFOAM/db/IOstreams/Fstreams/IFstream.H

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.C

src/OpenFOAM/db/IOstreams/Fstreams/OFstream.H

...nFOAM/global/fileOperations/fileOperation/fileOperation.C

...nFOAM/global/fileOperations/fileOperation/fileOperation.H

...erUncollatedFileOperation/masterUncollatedFileOperation.C

...erUncollatedFileOperation/masterUncollatedFileOperation.H

...rations/uncollatedFileOperation/uncollatedFileOperation.C

...rations/uncollatedFileOperation/uncollatedFileOperation.H

...ntial/pairPotential/pairPotentialList/pairPotentialList.C