Add Eq for Result (#6140)

## Description
Closes #6077

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: K1-R1 <77465250+K1-R1@users.noreply.github.com>

sway-lib-std/src/result.sw

@@ -269,3 +269,17 @@ impl<T, E> Result<T, E> {
     // - `ok(self) -> Option<T>`
     // - `err(self) -> Option<E>`
 }
+
+impl<T, E> Eq for Result<T, E>
+where
+    T: Eq,
+    E: Eq,
+{
+    fn eq(self, other: Self) -> bool {
+        match (self, other) {
+            (Self::Ok(a), Self::Ok(b)) => a == b,
+            (Self::Err(a), Self::Err(b)) => a == b,
+            _ => false,
+        }
+    }
+}

test/src/in_language_tests/test_programs/result_inline_tests/src/eq.sw

@@ -0,0 +1,114 @@
+library;
+
+#[test]
+fn test_eq_u64_u64() {
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Ok(0);
+    assert_eq(a, b);
+
+    let a: Result<u64, u64> = Ok(1);
+    let b: Result<u64, u64> = Ok(1);
+    assert_eq(a, b);
+
+    let a: Result<u64, u64> = Ok(42);
+    let b: Result<u64, u64> = Ok(42);
+    assert_eq(a, b);
+
+    let a: Result<u64, u64> = Ok(u64::max());
+    let b: Result<u64, u64> = Ok(u64::max());
+    assert_eq(a, b);
+}
+
+#[test]
+fn test_neq_u64_u64() {
+    // Ok
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Ok(1);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Ok(42);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Ok(u64::max());
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(1);
+    let b: Result<u64, u64> = Ok(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(42);
+    let b: Result<u64, u64> = Ok(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(u64::max());
+    let b: Result<u64, u64> = Ok(0);
+    assert_ne(a, b);
+
+    // Err
+    let a: Result<u64, u64> = Err(0);
+    let b: Result<u64, u64> = Err(1);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Err(0);
+    let b: Result<u64, u64> = Err(42);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Err(0);
+    let b: Result<u64, u64> = Err(u64::max());
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Err(1);
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Err(42);
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Err(u64::max());
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    // Ok-Err
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(1);
+    let b: Result<u64, u64> = Err(1);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(42);
+    let b: Result<u64, u64> = Err(42);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(u64::max());
+    let b: Result<u64, u64> = Err(u64::max());
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Err(1);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Err(42);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(0);
+    let b: Result<u64, u64> = Err(u64::max());
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(1);
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(42);
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+
+    let a: Result<u64, u64> = Ok(u64::max());
+    let b: Result<u64, u64> = Err(0);
+    assert_ne(a, b);
+}

test/src/in_language_tests/test_programs/result_inline_tests/src/main.sw

@@ -1,5 +1,7 @@
 library;
 
+mod eq;
+
 #[test]
 fn result_is_ok() {
     use std::bytes::Bytes;