refactor(ilp): strip QwpWebSocketSender of legacy SF / sync paths

QwpWebSocketSender now has a single send pipeline — the cursor SF engine.
The legacy WebSocketSendQueue + SegmentLog stack and the sync (window=1)
mode have no remaining callers, so the sender drops:

  * connect() overloads with SegmentLog / fsyncOnFlush parameters
  * setSegmentLog*, setSegmentLogFsyncOnFlush, setRequestDurableAck,
    getTotalSfDiskFullStalls, getHighestAckedSeqTxn,
    getHighestDurableSeqTxn, getMaxSentSymbolId, ping()
  * sync-mode flushSync, syncPing, waitForAck, AckFrameHandler,
    nextBatchSequence, sync*SeqTxns, sawPong/sawBinaryAck
  * SF reconnect machinery (performReconnect, schemaResetNeeded,
    connectionGeneration, MAX_SCHEMA_RACE_RETRIES retry loop)
  * sendQueue, segmentLog, ownsSegmentLog, fsyncOnFlush fields and
    inFlightWindow member

The remaining flow: ensureConnected wires up CursorWebSocketSendLoop;
flush()/close() drain through the cursor I/O thread; sealAndSwapBuffer
hands sealed buffers to engine.appendBlocking on the user thread.

The orphaned legacy source files (WebSocketSendQueue, InFlightWindow,
Reconnector, SegmentLog, SfDiskFullException, SfException) and the
sync-mode QwpWebSocketAckIntegrationTest are deleted in the same commit
since they no longer have any callers.

Net diff: ~4500 lines removed, ~125 added.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bluestreak01

core/src/main/java/io/questdb/client/Sender.java

@@ -1577,9 +1577,6 @@ public LineSenderBuilder protocolVersion(int protocolVersion) {
          * watermarks as WAL data reaches the object store.
          * <p>
          * This setting is only supported for WebSocket transport.
-         * <p>
-         * Observe durable progress via
-         * {@link QwpWebSocketSender#getHighestDurableSeqTxn(CharSequence)}.
          *
          * @param enabled true to request durable ACKs
          * @return this instance for method chaining