Rollup merge of #139750 - no1wudi:fix, r=tgross35

std/thread: Use default stack size from menuconfig for NuttX

* Update comments to clarify the usage of zero as an indication for default stack size configuration
* Adjust conditional compilation to reflect the changes in stack size handling for the NuttX platform

This change improves clarity and consistency in stack size configuration across platforms.

Author: Zalathar