feat: add ExpressibleByLiteral conformances to Length

Add ExpressibleByIntegerLiteral and ExpressibleByFloatLiteral to Length type
for cleaner API when constructing lengths from numeric literals.

Example usage:
  let width: W3C_SVG2.Types.Length = 100  // .number(100)
  let height: W3C_SVG2.Types.Length = 50.5  // .number(50.5)

This provides better ergonomics while maintaining type safety.

Author: coenttb

Sources/W3C SVG/W3C_SVG2.Types.Length.swift

@@ -102,3 +102,15 @@ extension W3C_SVG2.Types {
         }
     }
 }
+
+extension W3C_SVG2.Types.Length: ExpressibleByIntegerLiteral {
+    public init(integerLiteral value: Int) {
+        self = .number(.init(value))
+    }
+}
+
+extension W3C_SVG2.Types.Length: ExpressibleByFloatLiteral {
+    public init(floatLiteral value: Float) {
+        self = .number(.init(value))
+    }
+}