style(pwd): simplify physical_path implementation

[amirhosseinghanipour]

This pull request proposes a minor stylistic simplification for the physical_path function in the pwd utility.

The current implementation is perfectly correct and performant and correctly handles the platform-specific behaviors of env::current_dir(). It correctly avoids a redundant canonicalize() call on Unix while applying it on other platforms like Windows where it's necessary.

This PR suggests a small refactor to reduce code duplication. By calling env::current_dir() once and then using #[cfg] blocks to apply the canonicalize() call only where needed, the function becomes slightly more DRY.

Before:

fn physical_path() -> io::Result<PathBuf> {
    // std::env::current_dir() is a thin wrapper around libc::getcwd().

    // On Unix, getcwd() must return the physical path:
    // https://pubs.opengroup.org/onlinepubs/9699919799/functions/getcwd.html
    #[cfg(unix)]
    {
        env::current_dir()
    }

    // On Windows we have to resolve it.
    // On other systems we also resolve it, just in case.
    #[cfg(not(unix))]
    {
        env::current_dir().and_then(|path| path.canonicalize())
    }
}

After:

fn physical_path() -> io::Result<PathBuf> {
    // std::env::current_dir() is a thin wrapper around libc::getcwd().
    let path = env::current_dir()?;

    // On Unix, getcwd() must return the physical path:
    // https://pubs.opengroup.org/onlinepubs/9699919799/functions/getcwd.html
    #[cfg(unix)]
    {
        Ok(path)
    }

    // On Windows we have to resolve it.
    // On other systems we also resolve it, just in case.
    #[cfg(not(unix))]
    {
        path.canonicalize()
    }
}

I want to emphasize that this is purely a stylistic suggestion intended to enhance clarity. The functionality and performance are identical, as any modern compiler will optimize both versions to the same machine code. I recognize the original implementation is a very direct and efficient way to express the logic. This alternative is simply another valid approach that some developers may find cleaner.

Thank you for considering this minor improvement. I appreciate the high quality of the existing codebase.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)

[sylvestre]

it doesn't hurt to merge it but not sure it simplifies much