[Repo Assist] refactor: simplify splitAt 'rest' taskSeq to use while!

[github-actions]

🤖 This is an automated pull request from Repo Assist, an AI assistant.

Summary

The rest sequence produced by TaskSeq.splitAt used a manual go2 flag and an explicit MoveNextAsync pre-advance before its inner loop:

let rest = taskSeq {
    let mutable go2 = go

    if go2 then
        let! step = e.MoveNextAsync()
        go2 <- step

    while go2 do
        yield e.Current
        let! step = e.MoveNextAsync()
        go2 <- step
}

This is equivalent to a single while! e.MoveNextAsync() do guarded by the existing outer go flag (which already tracks whether the source was exhausted while filling first):

let rest = taskSeq {
    if go then
        while! e.MoveNextAsync() do
            yield e.Current
}

This follows the same while! idiom used throughout the codebase (e.g. tryTail, tryLast, lengthBy).

Correctness

Three cases:

Scenario	go	Current behaviour	New behaviour
Source exhausted before count	false	rest is empty	rest is empty (guard skips)
Source has ≥ count elements	true	Advance past first, yield remainder	while! does the same advance-then-yield
count = 0	true	Advance from start, yield all	Same

Test Status

• Build: ✅ dotnet build -c Release — succeeded (0 warnings, 0 errors)
• Tests: ✅ dotnet test -c Release — 5180 passed, 2 skipped (pre-existing infrastructure skips)
• Format: ✅ dotnet fantomas . --check — passed

Generated by 🌈 Repo Assist, see workflow run. Learn more.

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@97143ac59cb3a13ef2a77581f929f06719c7402a