[Repo Assist] perf: use while! in tryTail inner loop, removing redundant mutable go flag

[github-actions]

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

Summary

Converts the inner taskSeq loop in tryTail from the manual go-flag + initial-MoveNext pre-advance pattern to the idiomatic while! form.

Before

taskSeq {
    let mutable go = true
    let! step = e.MoveNextAsync()
    go <- step

    while go do
        yield e.Current
        let! step = e.MoveNextAsync()
        go <- step
}
|> Some

After

taskSeq {
    while! e.MoveNextAsync() do
        yield e.Current
}
|> Some

Context

This is part of a broader series (#382, #386) replacing the old manual pre-advance idiom with the idiomatic while! CE operator, which:

• Removes one mutable go bool per function
• Removes the initial let! step = e.MoveNextAsync(); go <- step before the loop
• Unifies style across the module

Scope

Single-function change: tryTail. No public API or behaviour change.

Trade-offs

None. Identical semantics, verified by the full test suite.

Test Status

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

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