FlushCDC Problem with arduino-pico core

### Operating System

Windows 10

### IDE version

1.8.19

### Board

Raspberry PICO

### ArduinoCore version

2.3.3

### TinyUSB Library version

1.14.1

### Sketch (attached txt file)

```
#include

void setup() {
Serial.begin(115200);
}

void loop() {
Serial.println("blink!");
delay(200);
}
```

### What happened ?

Even/odd loop iteration doesn't send data to PC. Data is stored in buffer and transferred on next loop cycle.

### How to reproduce ?

Compile and upload sketch with arduino-pico core with TinyUSB stack and open serial port monitor.

### Debug Log

_No response_

### Screenshots


Start by reproducing the behavior with the provided sketch on a Raspberry PICO using the arduino-pico core and TinyUSB stack, while monitoring the serial output. Trace the FlushCDC path and CDC buffering behavior; done means each Serial.println() iteration reaches the PC without being delayed until the next loop cycle, with the reproduction still passing.

Written by the indexing model from the issue text.