fix: replace lastBufStart with lastBufEnd in QueryStreamAsync

The old guard skipped DecodePartial whenever bufStart == lastBufStart
(no decode progress). But after a split-token, bufStart stays the same
while new packets keep arriving — so every subsequent packet was skipped
until EOM, causing all rows to arrive at once instead of streaming.

Fix: track lastBufEnd instead. Skip decode only when no new bytes have
arrived since the last attempt (zero-payload packet), which is the
correct and rare case. Every packet that adds bytes now triggers decode.

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

Author: vkuttyp

src/SqlDotnetty.MsSql/MsSqlConnection.cs

@@ -301,7 +301,7 @@ public async IAsyncEnumerable<SqlRow> QueryStreamAsync(
             var buffer   = new byte[8192];
             int bufEnd   = 0;    // exclusive end of valid data
             int bufStart = 0;    // start of unconsumed data (decode cursor)
-            int lastBufStart = -1; // detect no-progress: skip decode until more data arrives
+            int lastBufEnd = 0;  // detect no-progress: skip decode only if no new bytes arrived
 
             var colMeta = new List<TdsColumnMeta>();
             bool eom    = false;
@@ -340,19 +340,19 @@ public async IAsyncEnumerable<SqlRow> QueryStreamAsync(
                 }
 
                 // ── Decode as many complete tokens as possible ───────────────
-                // Skip decode if last call made no progress — we need more data first.
-                // Always decode on EOM so we don't miss the final tokens.
-                if (bufStart != lastBufStart || eom)
+                // Skip decode only when no new bytes have arrived since the last attempt
+                // (i.e. a zero-payload status packet). Always decode on EOM.
+                if (bufEnd > lastBufEnd || eom)
                 {
-                    lastBufStart = bufStart;
+                    lastBufEnd = bufEnd;
                     var (tokens, newOffset, newColMeta) =
                         TdsDecoder.DecodePartial(buffer, bufStart, bufEnd, colMeta);
 
                     bufStart = newOffset;
                     colMeta  = newColMeta;
 
                     // Compact when fully consumed to recycle buffer space.
-                    if (bufStart == bufEnd) { bufStart = bufEnd = 0; lastBufStart = -1; }
+                    if (bufStart == bufEnd) { bufStart = bufEnd = 0; lastBufEnd = 0; }
 
                     // ── Yield rows; raise info/error messages ────────────────────
                     foreach (var token in tokens)