Remove is-root crate (#9615)

# Description
This PR tries to remove `is-root` crate.

# User-Facing Changes
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---------

Co-authored-by: Stefan Holderbach <sholderbach@users.noreply.github.com>

crates/nu-command/src/experimental/is_admin.rs

@@ -1,4 +1,3 @@
-use is_root::is_root;
 use nu_protocol::ast::Call;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
@@ -48,3 +47,62 @@ impl Command for IsAdmin {
         ]
     }
 }
+
+/// Returns `true` if user is root; `false` otherwise
+fn is_root() -> bool {
+    is_root_impl()
+}
+
+#[cfg(unix)]
+fn is_root_impl() -> bool {
+    nix::unistd::Uid::current().is_root()
+}
+
+#[cfg(windows)]
+fn is_root_impl() -> bool {
+    use windows::Win32::{
+        Foundation::{CloseHandle, HANDLE},
+        Security::{GetTokenInformation, TokenElevation, TOKEN_ELEVATION, TOKEN_QUERY},
+        System::Threading::{GetCurrentProcess, OpenProcessToken},
+    };
+
+    let mut handle = HANDLE::default();
+    let mut elevated = false;
+
+    // Checks whether the access token associated with the current process has elevated privileges.
+    // SAFETY: `elevated` only touched by safe code.
+    // `handle` lives long enough, initialized, mutated as out param, used, closed with validity check.
+    // `elevation` only read on success and passed with correct `size`.
+    unsafe {
+        // Opens the access token associated with the current process.
+        if OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &mut handle).as_bool() {
+            let mut elevation = TOKEN_ELEVATION::default();
+            let mut size = std::mem::size_of::<TOKEN_ELEVATION>() as u32;
+
+            // Retrieves elevation token information about the access token associated with the current process.
+            // Call available since XP
+            // https://learn.microsoft.com/en-us/windows/win32/api/securitybaseapi/nf-securitybaseapi-gettokeninformation
+            if GetTokenInformation(
+                handle,
+                TokenElevation,
+                Some(&mut elevation as *mut TOKEN_ELEVATION as *mut _),
+                size,
+                &mut size,
+            )
+            .as_bool()
+            {
+                // Whether the token has elevated privileges.
+                // Safe to read as `GetTokenInformation` will not write outside `elevation` and it succeeded
+                // See: https://learn.microsoft.com/en-us/windows/win32/api/securitybaseapi/nf-securitybaseapi-gettokeninformation#parameters
+                elevated = elevation.TokenIsElevated != 0;
+            }
+        }
+
+        if !handle.is_invalid() {
+            // Closes the object handle.
+            CloseHandle(handle);
+        }
+    }
+
+    elevated
+}