Align set of supported functions with latest FSharp.Control.AsyncSeq

[dsyme]

FSharp.Control.AsyncSeq has added a lot of supported functions (here methods) which should also be supported here if possible

Repo Assist: Do this in multiple independent PRs bit by bit rather than all at once, and don't label PRs as "fixing" this issue until it's really all completed.

[github-actions]

🤖 This is an automated response from Repo Assist.

Here's a progress update on aligning FSharp.Control.TaskSeq with the latest FSharp.Control.AsyncSeq API.

What's already been done (open PRs)

Function	PR	Notes
TaskSeq.pairwise	#293 (open)	seq<'T * 'T> — pairs of adjacent elements
TaskSeq.scan / TaskSeq.scanAsync	#296 (open)	Fold that emits each intermediate accumulator state

Good next candidates

These are pure streaming operations — no buffering needed — making them a natural fit:

• unfold — ('State -> ('T * 'State) option) -> 'State -> TaskSeq<'T> and unfoldAsync variant. Dual of fold; generates a sequence from a seed state. AsyncSeq: AsyncSeq.unfold.

• windowed — int -> TaskSeq<'T> -> TaskSeq<'T[]>. Sliding window of size n; emits overlapping sub-arrays. AsyncSeq: AsyncSeq.windowed.

• reduce / reduceAsync — ('T -> 'T -> 'T) -> TaskSeq<'T> -> Task<'T>. Fold without an initial state; raises on empty sequence. Analogous to Seq.reduce.

• sumBy / averageBy / sumByAsync / averageByAsync — numeric aggregations. Currently missing; useful alongside maxBy/minBy.

Functions that would need full materialization

The following AsyncSeq functions require consuming the entire sequence into memory, which is a larger design decision:

• sortBy / sort — requires materializing to sort
• groupBy / countBy — requires materializing to group/count

These are worth discussing separately, as they change the memory profile of the library. For now the functions above (streaming) are likely the right priority.

I'll continue adding these incrementally per @dsyme's guidance — one concern per PR.

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