WIP: custom allocator/memory pool in HLT1

This introduces a custom allocator and fast event-local memory pool and uses it to remove [almost] all dynamic [de]allocation in HLT1 algorithms. See LHCb MR for more details.

Goes with LHCb!2313 (closed) and Rec!1845 (closed).

WIP because others are WIP

cc: @graven @nnolte @sstahl @ahennequ