Add functions to get topic name to publisher and subscriber (#194)

* feat: add rcl_subscription_get_topic_name to subscription.rs (#148)

* tested addition of rcl_subscription_get_topic_name (#148)

* add rcl_publisher_get_topic to publisher.rs (#148)

* compiling successfully

* added wrappers for rcl_publisher_get_topic_name and rcl_subscription_get_topic_name (#148)

* replaced if let with match for error handling (#148)

* changes made to formatting

* modified code to return String instead of Cow (#148)

* changed to_owned to into_owned (#148)

* returning String instead of Result (#148)

* grammar changes to comments (#148)

Author: DS3a

rclrs/src/node/publisher.rs

@@ -4,6 +4,7 @@ use crate::rcl_bindings::*;
 use crate::Node;
 
 use std::borrow::Cow;
+use std::ffi::CStr;
 use std::ffi::CString;
 use std::marker::PhantomData;
 use std::sync::Arc;
@@ -97,6 +98,21 @@ where
         })
     }
 
+    /// Returns the topic name of the publisher.
+    ///
+    /// This returns the topic name after remapping, so it is not necessarily the
+    /// topic name which was used when creating the publisher.
+    pub fn get_topic(&self) -> String {
+        // SAFETY: No preconditions for the functions called.
+        // The unsafe variables created get converted to safe types before being returned
+        unsafe {
+            let raw_topic_pointer = rcl_publisher_get_topic_name(&*self.handle.lock());
+            CStr::from_ptr(raw_topic_pointer)
+                .to_string_lossy()
+                .into_owned()
+        }
+    }
+
     /// Publishes a message.
     ///
     /// The [`MessageCow`] trait is implemented by any

rclrs/src/node/subscription.rs

@@ -4,6 +4,7 @@ use crate::Node;
 use crate::{rcl_bindings::*, RclrsError};
 
 use std::boxed::Box;
+use std::ffi::CStr;
 use std::ffi::CString;
 use std::marker::PhantomData;
 use std::sync::Arc;
@@ -124,6 +125,21 @@ where
         })
     }
 
+    /// Returns the topic name of the subscription.
+    ///
+    /// This returns the topic name after remapping, so it is not necessarily the
+    /// topic name which was used when creating the subscription.
+    pub fn get_topic(&self) -> String {
+        // SAFETY: No preconditions for the function used
+        // The unsafe variables get converted to safe types before being returned
+        unsafe {
+            let raw_topic_pointer = rcl_subscription_get_topic_name(&*self.handle.lock());
+            CStr::from_ptr(raw_topic_pointer)
+                .to_string_lossy()
+                .into_owned()
+        }
+    }
+
     /// Fetches a new message.
     ///
     /// When there is no new message, this will return a