[Repo Assist] feat: add TaskSeq.chunkBySize and TaskSeq.windowed (closes #258, ref #289)

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Summary

Adds two sequence-segmentation combinators that were explicitly requested (see #258 and the closing comment on #265) and are part of the Seq API alignment tracked in #289.

TaskSeq.chunkBySize

Divides a task sequence into non-overlapping chunks of at most chunkSize elements. The last chunk may be smaller if the source does not divide evenly.

taskSeq { yield! [1..7] }
|> TaskSeq.chunkBySize 3
// → [| [|1;2;3|]; [|4;5;6|]; [|7|] |]

Performance: uses a fixed-size pre-allocated 'T[] buffer instead of a ResizeArray, avoiding resize allocations. One Array.copy per full chunk, one Array.sub for the last partial chunk.

TaskSeq.windowed

Returns overlapping sliding windows of exactly windowSize consecutive elements.

taskSeq { yield! [1..5] }
|> TaskSeq.windowed 3
// → [| [|1;2;3|]; [|2;3;4|]; [|3;4;5|] |]

Performance: maintains a ring buffer of size windowSize — each new element is written in O(1) at the current position. When a full window is ready, two Array.blit calls copy it in source order to a fresh result array, giving a single allocation per window with no redundant element movement.

Both functions:

• Validate the size argument eagerly (before enumeration), raising ArgumentException for non-positive sizes — consistent with Seq.chunkBySize / Seq.windowed.
• Include full XML doc comments in the .fsi signature file.

Other changes

• README.md: marks chunkBySize, windowed, pairwise, scan/scanAsync, reduce/reduceAsync, and unfold/unfoldAsync as implemented (these were merged in PRs [Repo Assist] feat/test: add TaskSeq.pairwise; expand distinctUntilChanged tests #293, [Repo Assist] feat: add TaskSeq.scan and TaskSeq.scanAsync (ref #289) #296, [Repo Assist] feat: add TaskSeq.reduce and TaskSeq.reduceAsync (ref #289) #299, [Repo Assist] feat: add TaskSeq.unfold and TaskSeq.unfoldAsync (ref #289) #300 but the README wasn't updated).
• release-notes.txt: updated for 0.5.0.

Tests

TaskSeq.ChunkBySize.Tests.fs and TaskSeq.Windowed.Tests.fs — 171 new tests covering:

• Null / invalid argument handling (eager throws)
• Empty source variants (all TestEmptyVariants)
• All TestImmTaskSeq variants: order preservation, chunk/window sizes, remainder, exact-size, larger-than-source
• Array independence (mutating one chunk/window doesn't affect others)
• Side-effect execution
• Exception propagation from source
• Ring-buffer correctness (explicit wrap-around test for windowed)

Test Status

✅ Build: succeeded (0 warnings, 0 errors) — verified locally against .NET SDK 10.0.102
✅ Tests: 4,021 passed, 2 skipped, 0 failed (full suite)
✅ Formatting: dotnet fantomas . --check passes

Note: global.json pins SDK 10.0.103; CI on windows-latest will run with the exact pinned version.

Closes #258

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