Add support for 32-bit architecture
Adds some casts and changes
m_cacheSize to a
off_t to allow compilation on 32-bit systems. Switch to UNIX I/O to allow transfer of files larger than 4 GiB. Adds test to ensure this is the case. Note there is a kernel bug that means that transferring files larger than 4 GiB on 32-bit systems via KIOFuse is likely to result in data corruption. Use kernel versions older than 5.1.5+ to eliminate the possibility of data corruption.