Validate input range of du flags (#7962)

# Description
Fix #7953
Fix flags on `du` which should be positive and added some tests. 

# User-Facing Changes

_(List of all changes that impact the user experience here. This helps
us keep track of breaking changes.)_

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/tests/commands/platform/du.rs

@@ -0,0 +1,43 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn test_du_flag_min_size() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            du -m -1
+        "#
+    ));
+    assert!(actual
+        .err
+        .contains("Negative value passed when positive one is required"));
+
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            du -m 1
+        "#
+    ));
+    assert!(actual.err.is_empty());
+}
+
+#[test]
+fn test_du_flag_max_depth() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            du -d -2
+        "#
+    ));
+    assert!(actual
+        .err
+        .contains("Negative value passed when positive one is required"));
+
+    let actual = nu!(
+        cwd: "tests/fixtures/formats", pipeline(
+        r#"
+            du -d 2
+        "#
+    ));
+    assert!(actual.err.is_empty());
+}

crates/nu-command/tests/commands/platform/mod.rs

@@ -1 +1,2 @@
+mod du;
 mod kill;