[BUG] system/popen memcpy FILE

[yamt]

Description / Steps to reproduce the issue

for some reasons, system/popen memcpy a FILE.
it seems fragile at best to me.
it should not assume libc FILE implementation details.

On which OS does this issue occur?

[OS: Mac]

What is the version of your OS?

macOS 15.2

NuttX Version

master

Issue Architecture

[Arch: all]

Issue Area

[Area: System]

Verification

• I have verified before submitting the report.