Add numeral extraction helpers to Java API

New methods:
- Expr.getNumeralDouble(): retrieve any numeral as a double
- IntNum.getUint(): extract numeral as unsigned 32-bit value
- IntNum.getUint64(): extract numeral as unsigned 64-bit value
- RatNum.getSmall(): numerator/denominator as int64 pair
- RatNum.getRationalInt64(): numerator/denominator (returns null on overflow)

Each is a thin wrapper around the existing Native binding.
Added examples to JavaExample.java covering all new methods.

src/api/java/Expr.java

@@ -244,6 +244,15 @@ public class Expr<R extends Sort> extends AST
         return Native.isNumeralAst(getContext().nCtx(), getNativeObject());
     }
 
+    /**
+     * Return the numeral value as a double.
+     * The expression must be a numeral or an algebraic number.
+     **/
+    public double getNumeralDouble()
+    {
+        return Native.getNumeralDouble(getContext().nCtx(), getNativeObject());
+    }
+
     /**
      * Indicates whether the term is well-sorted.
      *