[Repo Assist] perf: direct loop in toResizeArrayAsync; simplify tryItem loop

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Summary

Two small, focused performance improvements to TaskSeqInternal.fs.

1. toResizeArrayAsync — direct loop instead of iter

Before:

let toResizeArrayAsync source =
    checkNonNull (nameof source) source
    task {
        let res = ResizeArray()
        do! source |> iter (SimpleAction(fun item -> res.Add item))
        return res
    }

After:

let toResizeArrayAsync (source: TaskSeq<'T>) =
    checkNonNull (nameof source) source
    task {
        let res = ResizeArray<'T>()
        use e = source.GetAsyncEnumerator CancellationToken.None
        while! e.MoveNextAsync() do
            res.Add e.Current
        return res
    }

Why it's faster: the old code created a lambda closure (fun item -> res.Add item), wrapped it in a SimpleAction discriminated-union case (a heap allocation), then called iter which pattern-matched on the DU and drove a manual go-flag loop. The new code does none of that.

Scope: toResizeArrayAsync is the implementation shared by toArrayAsync, toListAsync, toResizeArrayAsync, and toIListAsync, so all four terminal operations benefit.

---

2. tryItem — remove redundant inner index check

Before:

while go && idx <= index do
    if idx = index then
        foundItem <- Some e.Current
        go <- false
    else
        let! step = e.MoveNextAsync()
        go <- step
        idx <- idx + 1

After:

// advance past the first `index` elements, then capture the current element
while go && idx < index do
    let! step = e.MoveNextAsync()
    go <- step
    idx <- idx + 1

if go then
    foundItem <- Some e.Current

Why it's faster: the old loop condition idx <= index meant the if idx = index branch ran on every iteration (not just the last one). The refactored version moves the capture outside the loop, so there's no per-iteration inner comparison.

---

Trade-offs

• Both changes are purely internal — no public API or behaviour change.
• The toResizeArrayAsync change also removes the dependency on iter for this use-case, which improves code clarity.

Test Status

✅ Build: 0 warnings, 0 errors (Release)
✅ Fantomas: formatting check passes
✅ Tests: 5093 passed, 2 skipped, 0 failed

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