Remove deprecated code warnings and minor perf improvements

[cryptonemo]

Aims to resolve #1435 and investigate #1426

[dignifiedquire]

you should be able to collect into Result<Vec>> allowing you to acutally handle the error, instead of expecting

[cryptonemo]

Maybe I'm missing something, but it looks like not what I want. The return type is Result<Vec<Column<Tree::Hasher>>>, but w/o the expect, we'd be returning Vec<Result<Column<Tree::Hasher>>>.

[dignifiedquire]

parents
  .into_par_iter()
  .map(|parent| t_aux.column(parent))
  .collect::<Result<Vec<Column<Tree::Hasher>>, _>>()?

is what I have in mind, to avoid the expect

[cryptonemo]

Hrm, that makes sense, I think I had simply noted the difference of return type if the expect was removed, not changing the collect type. Is there a difference between:

.collect::<Result<Vec<Column<Tree::Hasher>>, _>>()?

and

.collect::<Result<Vec<Column<Tree::Hasher>>>()?

They both appear to work.

[cryptonemo]

They both appear to work.

Nevermind, just seems to be the type of error, which is implied either way (explicitly or implicitly).

[cryptonemo]

Rebased against master