us ticker read - should not return timestamp_t type?

As the title says, us_ticker_read() should probably return timestamp_t return value.

```
/** Read the current counter
*
* @return The current timer's counter value in microseconds
*/
uint32_t us_ticker_read(void);

/** Set interrupt for specified timestamp
*
* @param timestamp The time in microseconds to be set
*/
void us_ticker_set_interrupt(timestamp_t timestamp);
```

Locate the declarations and implementations of us_ticker_read() and us_ticker_set_interrupt(), then compare their timestamp types and documentation. Check the surrounding mbed HAL API for compatibility expectations; the work is done when the read API consistently uses the intended timestamp type and related checks remain valid.

Written by the indexing model from the issue text.