Fixes compiler asking for unnecessary disambiguation for trait methods. (#5801)

## Description

`find_method_for_type` was throwing an error when multiple
implementations of a method exist receiving different kinds of unsigned
int. This was caused by the coercion comparison which returned true
while comparing any uint size to any other uint size.

The solution was to change the UnifyCheck on Coercion to only return
true to same size uints.

Fixes #5798

## 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.
- [x] 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).
- [x] I have requested a review from the relevant team or maintainers.

Co-authored-by: Joshua Batty <joshpbatty@gmail.com>

Author: esdrubal

sway-core/src/type_system/unify/unify_check.rs

@@ -375,7 +375,7 @@ impl<'a> UnifyCheck<'a> {
                     (Unknown, _) => true,
                     (_, Unknown) => true,
 
-                    (UnsignedInteger(_), UnsignedInteger(_)) => true,
+                    (UnsignedInteger(lb), UnsignedInteger(rb)) => lb == rb,
                     (Numeric, UnsignedInteger(_)) => true,
                     (UnsignedInteger(_), Numeric) => true,
 

test/src/e2e_vm_tests/test_programs/should_pass/language/method_unambiguous/Forc.lock

@@ -0,0 +1,13 @@
+[[package]]
+name = "core"
+source = "path+from-root-13393DAFAC4DB2CA"
+
+[[package]]
+name = "method_unambiguous"
+source = "member"
+dependencies = ["std"]
+
+[[package]]
+name = "std"
+source = "path+from-root-13393DAFAC4DB2CA"
+dependencies = ["core"]

test/src/e2e_vm_tests/test_programs/should_pass/language/method_unambiguous/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <contact@fuel.sh>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "method_unambiguous"
+
+[dependencies]
+std = { path = "../../../../../../../sway-lib-std" }

test/src/e2e_vm_tests/test_programs/should_pass/language/method_unambiguous/src/main.sw

@@ -0,0 +1,27 @@
+script;
+
+use std::convert::From;
+
+impl From<u8> for u256 {
+    fn from(num: u8) -> Self {
+        num.as_u256()
+    }
+}
+
+impl From<u16> for u256 {
+    fn from(num: u16) -> Self {
+        num.as_u256()
+    }
+}
+
+fn main() -> u64 {
+    use std::assert::assert;
+
+    let u256_value = u256::from(255_u8);
+    assert(u256_value == 0x00000000000000000000000000000000000000000000000000000000000000ff_u256);
+
+    let u256_value = u256::from(65535_u16);
+    assert(u256_value == 0x000000000000000000000000000000000000000000000000000000000000ffff_u256);
+
+    1
+}

test/src/e2e_vm_tests/test_programs/should_pass/language/method_unambiguous/test.toml

@@ -0,0 +1,3 @@
+category = "run"
+expected_result = { action = "return", value = 1 }
+validate_abi = false