Fix warnings introduced by mCBM MRs + some similar ones
- Fix mismatch in old MQ samplers with current flesnet IPC, removing warnings
- Fix new sign warnings introduced by mCBM MRs
- Fix deprecation warning for ROOT serdes method in old Histo Server MQ device
- Fix unused variable warnings introduced by mCBM MRs
Probably complementary of !863 (closed) (but should be fixing only new warnings)