WIP: Fix non-tensor scalar result aggregation

[s-rog]

What does this PR do?

Fixes #3276
Resolves #2143

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Todo

ddp sync for converted tensors?
convert in log or __set_meta?
write test(s)
fix tests

[s-rog]

@justusschock any thoughts on the first two entries in my todo above?

[justusschock]

@s-rog I'd say convert ASAP and maybe the ddp_sync should come automatically with that

[s-rog]

@justusschock gotcha, I just put it there for now to maintain current (no) syncing behavior, update to come

[codecov]

Codecov Report

Merging #3540 into master will decrease coverage by 0%.
The diff coverage is 67%.

@@          Coverage Diff           @@
##           master   #3540   +/-   ##
======================================
- Coverage      91%     91%   -0%     
======================================
  Files         109     109           
  Lines        8043    8045    +2     
======================================
+ Hits         7303    7304    +1     
- Misses        740     741    +1     

[s-rog]

I'm trying to figure out why the code path is different for results between tests and examples, as the changes fixes the issue correctly in examples but seem to have no effect in tests (no casting occurs).

Edit:
I'm occupied by a project atm, will continue working on this as soon as I can.

[edenlightning]

@williamFalcon any advice?

[Borda]

fixed in #3855