clock() and CLOCKS_PER_SEC is not POSIX compliant

NuttX defines `CLOCKS_PER_SEC` as:

```
#ifdef CONFIG_USEC_PER_TICK
# define CLK_TCK (1000000/CONFIG_USEC_PER_TICK)
# define CLOCKS_PER_SEC (1000000/CONFIG_USEC_PER_TICK)
#else
# define CLK_TCK (100)
# define CLOCKS_PER_SEC (100)
#endif
```
But the POSIX standard defines it as always one million.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html

Start by locating the clock() implementation and the definitions of CLOCKS_PER_SEC and CLK_TCK, then read the linked POSIX specification to compare their required meanings. Done means the exposed clock timing interface follows the specified CLOCKS_PER_SEC behavior across the relevant configuration paths, with existing clock-related tests or checks updated as needed.

Written by the indexing model from the issue text.