Fix clippy::items_after_test_module warning

```
error: items after a test module
   --> tf_rosrust/src/transforms.rs:136:1
    |
136 |   mod test {
    |   ^^^^^^^^
...
217 | / pub(crate) fn to_transform_stamped(
218 | |     tf: Transform,
219 | |     from: std::string::String,
220 | |     to: std::string::String,
221 | |     time: rosrust::Time,
222 | | ) -> TransformStamped {
    | |_____________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#items_after_test_module
    = note: `-D clippy::items-after-test-module` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::items_after_test_module)]`
    = help: move the items to before the test module was defined
```

tf_r2r/src/transforms.rs

@@ -122,6 +122,22 @@ pub fn interpolate(t1: Transform, t2: Transform, weight: f64) -> Transform {
     }
 }
 
+pub(crate) fn to_transform_stamped(
+    tf: Transform,
+    from: std::string::String,
+    to: std::string::String,
+    time: &r2r::builtin_interfaces::msg::Time,
+) -> TransformStamped {
+    TransformStamped {
+        header: Header {
+            frame_id: from,
+            stamp: time.clone(),
+        },
+        child_frame_id: to,
+        transform: tf,
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -203,19 +219,3 @@ mod test {
         assert_eq!(interpolate(tf1, tf2, 0.5), expected);
     }
 }
-
-pub(crate) fn to_transform_stamped(
-    tf: Transform,
-    from: std::string::String,
-    to: std::string::String,
-    time: &r2r::builtin_interfaces::msg::Time,
-) -> TransformStamped {
-    TransformStamped {
-        header: Header {
-            frame_id: from,
-            stamp: time.clone(),
-        },
-        child_frame_id: to,
-        transform: tf,
-    }
-}

tf_rosrust/src/transforms.rs

@@ -132,6 +132,23 @@ pub fn interpolate(t1: Transform, t2: Transform, weight: f64) -> Transform {
     }
 }
 
+pub(crate) fn to_transform_stamped(
+    tf: Transform,
+    from: std::string::String,
+    to: std::string::String,
+    time: rosrust::Time,
+) -> TransformStamped {
+    TransformStamped {
+        header: Header {
+            frame_id: from,
+            stamp: time,
+            seq: 1u32,
+        },
+        child_frame_id: to,
+        transform: tf,
+    }
+}
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -213,20 +230,3 @@ mod test {
         assert_eq!(interpolate(tf1, tf2, 0.5), expected);
     }
 }
-
-pub(crate) fn to_transform_stamped(
-    tf: Transform,
-    from: std::string::String,
-    to: std::string::String,
-    time: rosrust::Time,
-) -> TransformStamped {
-    TransformStamped {
-        header: Header {
-            frame_id: from,
-            stamp: time,
-            seq: 1u32,
-        },
-        child_frame_id: to,
-        transform: tf,
-    }
-}