Ensure that subscripting AttributeSliceX behaves consistently regardless of index location

Sources/FoundationEssentials/AttributedString/AttributedString+Runs.swift

@@ -594,9 +594,6 @@ extension AttributedString.Runs {
         // _strBounds.range(containing:) below validates that i._value is within the bounds of this slice
         precondition(!attributeNames.isEmpty)
         let r = _guts.findRun(at: i._value)
-        if r.runIndex.offset == endIndex._runOffset {
-            return (i, r.runIndex)
-        }
         let currentRange = _strBounds.range(containing: i._value).range
 
         guard constraints.count != 1 || constraints.contains(nil) else {

Tests/FoundationEssentialsTests/AttributedString/AttributedStringTests.swift

@@ -1983,6 +1983,34 @@ E {
             }
         }
     }
+
+    @Test func runSliceSubscripting() {
+        var str = AttributedString("Foo", attributes: .init().testInt(1))
+        str += AttributedString("Bar", attributes: .init().testInt(2))
+        str += AttributedString("Baz", attributes: .init().testInt(3))
+
+        do {
+            let runsSlice = str.runs[\.testInt]
+            for (value, range) in runsSlice {
+                for idx in str.utf8[range].indices {
+                    let subscriptResult = runsSlice[idx]
+                    #expect(subscriptResult.0 == value, "Subscript index \(idx) did not produce same value as runs slice")
+                    #expect(subscriptResult.1 == range, "Subscript index \(idx) did not produce same range as runs slice")
+                }
+            }
+        }
+
+        do {
+            let runsSlice = str[str.index(afterCharacter: str.startIndex) ..< str.index(beforeCharacter: str.endIndex)].runs[\.testInt]
+            for (value, range) in runsSlice {
+                for idx in str.utf8[range].indices {
+                    let subscriptResult = runsSlice[idx]
+                    #expect(subscriptResult.0 == value, "Subscript index \(idx) did not produce same value as runs slice")
+                    #expect(subscriptResult.1 == range, "Subscript index \(idx) did not produce same range as runs slice")
+                }
+            }
+        }
+    }
 
     // MARK: - Other Tests