feat: add rust solution to lc problem: No.2490 (#1305)

Signed-off-by: xiaolatiao <1628652790@qq.com>

Author: dierbei

solution/2400-2499/2490.Circular Sentence/README.md

@@ -303,6 +303,27 @@ impl Solution {
 }
 ```
 
+```rust
+impl Solution {
+    pub fn is_circular_sentence(sentence: String) -> bool {
+        let n = sentence.len();
+        let chars: Vec<char> = sentence.chars().collect();
+        
+        if chars[0] != chars[n - 1] {
+            return false;
+        }
+
+        for i in 1..n - 1 {
+            if chars[i] == ' ' && chars[i - 1] != chars[i + 1] {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+```
+
 ### **...**
 
 ```

solution/2400-2499/2490.Circular Sentence/README_EN.md

@@ -281,6 +281,27 @@ impl Solution {
 }
 ```
 
+```rust
+impl Solution {
+    pub fn is_circular_sentence(sentence: String) -> bool {
+        let n = sentence.len();
+        let chars: Vec<char> = sentence.chars().collect();
+        
+        if chars[0] != chars[n - 1] {
+            return false;
+        }
+
+        for i in 1..n - 1 {
+            if chars[i] == ' ' && chars[i - 1] != chars[i + 1] {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+```
+
 ### **...**
 
 ```