refactor: simplify splitAt 'rest' taskSeq to use while!

The 'rest' sequence returned by splitAt used a manual go2 flag and an
explicit MoveNextAsync pre-advance before its loop.  This is equivalent
to a direct 'while! e.MoveNextAsync() do yield e.Current' guarded by
the existing 'go' flag (which tracks whether the source was exhausted
while filling 'first').

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

release-notes.txt

@@ -2,6 +2,7 @@
 Release notes:
 
 Unreleased
+    - refactor: simplify splitAt 'rest' taskSeq to use while!, removing redundant go2 mutable and manual MoveNextAsync pre-advance
 
 1.1.1
     - perf: use while! in groupBy, countBy, partition, except, exceptOfSeq to eliminate redundant mutable 'go' variables and initial MoveNextAsync calls

src/FSharp.Control.TaskSeq/TaskSeqInternal.fs

@@ -848,18 +848,12 @@ module internal TaskSeqInternal =
                 else
                     go <- false
 
-            // 'rest' captures 'e' from the outer task block, following the same pattern as tryTail.
+            // 'rest' captures 'e' from the outer task block; if the source was not exhausted,
+            // advance once past the last element added to 'first', then yield the remainder.
             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
+                if go then
+                    while! e.MoveNextAsync() do
+                        yield e.Current
             }
 
             return first.ToArray(), rest