Added changes for ls-l time support

[Biancaa-R]

Fixes the issue : apache/nuttx#17063

a) modification aims to add human-readable timestamp reporting to the ls command by utilizing the struct stat information.
b) time_t st_mtime; / Time of last modification / from stat register to maintain time records.
c) Epoch entries replaced by ---.
d) ls -l (without options) implementation done here.

Note: Please adhere to Contributing Guidelines.

Summary

• So basically displaying the last modified time that is stored in the stat struct in ls -l command.
• stat(fullpath, &buf): This fills the buf structure with metadata from the filesystem.
• buf.st_mtime: This specifically targets the "Last Modified" timestamp.
• Safety Check: if (ret == 0 && buf.st_mtime > 0 ...) ensures that the stat call was successful and that the time value is valid before trying to process it.
• localtime_r(&t, &tm): This takes the Unix epoch time (seconds since 1970) and breaks it down into a struct tm (years, months, days, etc.).
• Formatting: %04d-%02d-%02d, which outputs the ISO 8601 standard (e.g., 2023-10-27).

Impact

Previously the ls -l didnt display the time of last modification , this is a small fix for more "linux like" experience.

Testing

• Apache NuttX Simulation Mode allows you to run the OS as a native Linux process.
• Building and running it and executing the ls -l command in the shell.

[cederom]

Thank you @Biancaa-R :-) Can you please provide output of ls -l command from Linux/Unix shell and ls -l from nsh after your change? Are these outputs comparable for parse (i.e. information order) :-)

[linguini1]

Hi! To fix the CI errors, please run ./tools/checkpatch.sh on your changes and fix the issues.

[cederom]

CI build failed.