Move generate_series projection logic into LazyMemoryStream

[mkleen]

Which issue does this PR close?

• None, This is a follow-up for Fix: Add projection to generate_series #18298

Rationale for this change

This moves the projection logic from generate_series out of the generator into LazyMemoryStream as discussed in #18298 (comment) This makes the projection logic generic for all generators.

What changes are included in this PR?

The projection logic is moved from generate_series into the LazyMemoryStream and relevant tests, where LazyMemoryStream is used, are adapted accordingly.

Are these changes tested?

This is only a small refactoring; the changes are covered by the tests from #18298

Are there any user-facing changes?

There is a new parameter added to LazyMemoryExec::try_new method

[alamb]

Thank you @mkleen -- this looks like a nice cleanup to me

I have one comment on the API -- let me know what you think

[alamb]

this is technically a breaking API change -- it is minor but still breaking

What would you think about adding a new method like

impl LazyMemoryExec {
  pub fn with_projection(projection: Option<Vec<usize>>) -> Self { ... }
}

instead and leave the signature of try_new the same

That would avoid the API breakage (and likely reduce the size of this PR a bit as many callsites would not have to be changed)

[mkleen]

I agree, thanks for the feedback.