DPL: cleanup and speedups using neat optimizations based on vtune insights

[mina1460]

• replacing grid_info_map.at with grid_info_vector.at reduces runtime from 1 second on aes to 0.22 seconds and removed this: dpl::GridMapKey::operator< 0.220s
• caching the getSite function in the cell results in significant gains by removing all of these db calls

odb::dbTable<odb::_dbInstHdr>::getPtr 0.280s
odb::_dbObject::getObjectPage   0.240s
odb::dbTable<odb::_dbLib>::getPtr 0.220s
odb::_dbObject::getOwner 0.200s 

to only 1 : odb::_dbObject::getObjectPage 0.164s

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"