Fix wasm32v1-none compilation errors

- arrayvec.rs: Use concrete return types ([T], slice::Iter, slice::IterMut)
  instead of Self::Target/Self::IntoIter to avoid E0223 ambiguity
  introduced by the Receiver trait in Rust 1.87+
- char.rs: Explicitly import Result/Ok/Err from core for target_os=none
  where the standard prelude is not auto-injected

tests/serde.rs

@@ -0,0 +1,79 @@
+#![cfg(feature = "serde")]
+extern crate arrayvec;
+extern crate serde_test;
+
+mod array_vec {
+    use arrayvec::ArrayVec;
+
+    use serde_test::{Token, assert_tokens, assert_de_tokens_error};
+
+    #[test]
+    fn test_ser_de_empty() {
+        let vec = ArrayVec::<u32, 0>::new();
+
+        assert_tokens(&vec, &[
+            Token::Seq { len: Some(0) },
+            Token::SeqEnd,
+        ]);
+    }
+
+
+    #[test]
+    fn test_ser_de() {
+        let mut vec = ArrayVec::<u32, 3>::new();
+        vec.push(20);
+        vec.push(55);
+        vec.push(123);
+
+        assert_tokens(&vec, &[
+            Token::Seq { len: Some(3) },
+            Token::U32(20),
+            Token::U32(55),
+            Token::U32(123),
+            Token::SeqEnd,
+        ]);
+    }
+
+    #[test]
+    fn test_de_too_large() {
+        assert_de_tokens_error::<ArrayVec<u32, 2>>(&[
+            Token::Seq { len: Some(3) },
+            Token::U32(13),
+            Token::U32(42),
+            Token::U32(68),
+        ], "invalid length 3, expected an array with no more than 2 items");
+    }
+}
+
+mod array_string {
+    use arrayvec::ArrayString;
+
+    use serde_test::{Token, assert_tokens, assert_de_tokens_error};
+
+    #[test]
+    fn test_ser_de_empty() {
+        let string = ArrayString::<0>::new();
+
+        assert_tokens(&string, &[
+            Token::Str(""),
+        ]);
+    }
+
+
+    #[test]
+    fn test_ser_de() {
+        let string = ArrayString::<9>::from("1234 abcd")
+            .expect("expected exact specified capacity to be enough");
+
+        assert_tokens(&string, &[
+            Token::Str("1234 abcd"),
+        ]);
+    }
+
+    #[test]
+    fn test_de_too_large() {
+        assert_de_tokens_error::<ArrayString<2>>(&[
+            Token::Str("afd")
+        ], "invalid length 3, expected a string no more than 2 bytes long");
+    }
+}