Fix NimBLE_Stream_Server NUS compatibility: use standard two-characteristic layout

[Copilot]

The NimBLE_Stream_Server example used NUS UUIDs but a single characteristic for both notify (TX) and write (RX), which is non-standard and breaks compatibility with NUS terminal apps (nRF UART, Serial Bluetooth Terminal, etc.). Standard NUS requires separate TX (6E400003, notify) and RX (6E400002, write) characteristics.

No library code was changed. The existing NimBLEStreamServer::begin(pChr) already activates only the directions supported by the characteristic's properties — a NOTIFY-only characteristic enables the TX buffer; a WRITE-only characteristic enables the RX buffer — making the two-characteristic NUS pattern achievable entirely in the examples.

Example updates

NimBLE_Stream_Server

• Creates the NUS service and both characteristics manually
• Uses two NimBLEStreamServer instances backed by the appropriate characteristic:
  • bleStreamTx.begin(pTxChar) — NOTIFY-only char → TX-only stream (sends notifications)
  • bleStreamRx.begin(pRxChar) — WRITE-only char → RX-only stream (receives client writes)
• bleStreamTx.ready() tracks the subscribed client; bleStreamRx.available()/read() handles incoming data

NimBLECharacteristic* pTxChar = pSvc->createCharacteristic(TX_CHAR_UUID, NIMBLE_PROPERTY::NOTIFY);
NimBLECharacteristic* pRxChar = pSvc->createCharacteristic(RX_CHAR_UUID,
                                                           NIMBLE_PROPERTY::WRITE | NIMBLE_PROPERTY::WRITE_NR);
bleStreamTx.begin(pTxChar);
bleStreamRx.begin(pRxChar);

NimBLE_Stream_Client

• One NimBLEStreamClient for TX: writes to the server's RX characteristic (6E400002, WRITE_NR)
• Subscribes directly to the server's TX characteristic (6E400003) via pTxChar->subscribe() for RX, with an onServerNotify callback

bleStream.begin(pRxChar, false);           // TX: write to server's RX char
pTxChar->subscribe(true, onServerNotify);  // RX: receive notifications from server's TX char

NimBLE_Stream_Echo (custom UUIDs, single characteristic) is unchanged.

[h2zero]

This should be doable with only a change to the examples, no need for extra code in the class.

[Copilot]

This should be doable with only a change to the examples, no need for extra code in the class.

Done in commit 64c5111 — no library changes at all. The existing begin(pChr) already activates only the directions the characteristic supports (NOTIFY → TX buffer, WRITE → RX buffer), so using two NimBLEStreamServer instances is all that's needed on the server side. The client uses one NimBLEStreamClient for TX and a direct pTxChar->subscribe() callback for RX.