gramine [LibOS] Implement utime, utimes, utimensat

Description of the changes

This PR implements support for the utime(), utimes(), and utimensat() syscalls in Gramine to provide file timestamp update functionality. The utime() syscall is fully implemented, while utimes() and utimensat() are stubbed with equivalent behavior. These additions enhance Gramine's syscall compatibility and enable several LTP test cases that were previously skipped due to the lack of utimensat() support. The implementation retains the existing data types for atime, mtime, and ctime in the LibOS file structure, resulting in a timestamp resolution of one second. I took reference of prior discussions (PR #1144 and discussion #942) and implemented with lower resolution to keep the implementation minimal.