[Repo Assist] Add AsyncSeq.min, max, minBy, maxBy, minByAsync, maxByAsync

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Summary

Adds six new aggregation combinators that mirror Seq.min / Seq.max / Seq.minBy / Seq.maxBy:

AsyncSeq.min       : source:AsyncSeq<'T>                            -> Async<'T>   when 'T : comparison
AsyncSeq.max       : source:AsyncSeq<'T>                            -> Async<'T>   when 'T : comparison
AsyncSeq.minBy     : projection:('T -> 'Key) -> source:AsyncSeq<'T> -> Async<'T>  when 'Key : comparison
AsyncSeq.maxBy     : projection:('T -> 'Key) -> source:AsyncSeq<'T> -> Async<'T>  when 'Key : comparison
AsyncSeq.minByAsync: projection:('T -> Async<'Key>) -> source:AsyncSeq<'T> -> Async<'T>  when 'Key : comparison
AsyncSeq.maxByAsync: projection:('T -> Async<'Key>) -> source:AsyncSeq<'T> -> Async<'T>  when 'Key : comparison

All six raise InvalidOperationException on empty sequences, matching the behaviour of the corresponding Seq functions.

Implementation Notes

• Built on top of foldAsync with an option accumulator — no new enumerator boilerplate.
• min/max delegate to minBy id / maxBy id.
• Fixes a latent shadowing issue in bufferByTime: the existing Async.Sleep (max 0 rt) call was shadowed by the new max definition, and has been qualified as Operators.max 0 rt.

Test Status

All 202 tests pass ✅ (8 new tests added covering: correct min/max, async projections, empty-sequence errors for min and max).

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[github-actions]

Pull request created: #243