[ #31203 ] Clean a model mess and (try) to make it faster

Apparently, the old code path, while dodgy, was a little faster than the new one.
No idea why
[ #31203 ] Remove the last 'indexOf' from ContactProxyModel
[ #31178 ] Add new canvas item manager

This thing is military grade bullet proof code, it may be a little
overkill, but it will solve canvas item concurency problem once
and for all.