Fix Swift type inference issue for Xcode 26.4 beta (#604)

## Summary
- Adds an explicit `: Wrapped` type annotation to
`Optional+Extensions.swift` to fix a type inference regression in the
Xcode 26.4 beta Swift compiler.

## Test plan
- [x] Verified the file compiles with
`DEVELOPER_DIR=/Applications/Xcode-26.4.0-Beta.app swiftc`

Author: timsutton

BlueprintUIAccessibilityCore/Sources/Extensions/Optional+Extensions.swift

@@ -3,7 +3,7 @@ import Foundation
 extension Optional where Wrapped: RangeReplaceableCollection {
 
     static func + (left: Wrapped?, right: Wrapped?) -> Wrapped? {
-        let val = (left ?? Wrapped()) + (right ?? Wrapped())
+        let val: Wrapped = (left ?? Wrapped()) + (right ?? Wrapped())
         return val.isEmpty ? nil : val
     }