Implement PartialEq for ConcatenatedStringLiteral

As highlighted in the review:

> If you have two `ConcatenatedStringLiteral` values where both have
> equivalent values for `strings` but where one has `value` initialized
> and the other does not, would you expect them to compare equal?
> Semantically I think I would, since the alternative is that equality is
> dependent on whether `as_str()` has been called, which seems incidental.

#7927 (comment)

crates/ruff_python_ast/src/nodes.rs

@@ -1306,7 +1306,7 @@ impl From<StringLiteral> for Expr {
 
 /// An internal representation of [`StringLiteral`] that represents an
 /// implicitly concatenated string.
-#[derive(Clone, PartialEq)]
+#[derive(Clone)]
 struct ConcatenatedStringLiteral {
     /// Each string literal that makes up the concatenated string.
     strings: Vec<StringLiteral>,
@@ -1322,6 +1322,19 @@ impl ConcatenatedStringLiteral {
     }
 }
 
+impl PartialEq for ConcatenatedStringLiteral {
+    fn eq(&self, other: &Self) -> bool {
+        if self.strings.len() != other.strings.len() {
+            return false;
+        }
+        // The `zip` here is safe because we have checked the length of both parts.
+        self.strings
+            .iter()
+            .zip(other.strings.iter())
+            .all(|(s1, s2)| s1 == s2)
+    }
+}
+
 impl Debug for ConcatenatedStringLiteral {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("ConcatenatedStringLiteral")