fix(BArrayType): Fix unnamed union array types printing in diagnostics

[Atharva1723]

Purpose

When printing array types whose element type is an unnamed union, diagnostics
previously displayed them without parentheses (e.g., '1|2|3[]') instead of
the correct '(1|2|3)[]'. This could lead to confusion when reading type errors.

Fixes ##35018

Approach

• Updated BArrayType.toString() to wrap unnamed unions in parentheses.
• Ensured diagnostic printing uses the same string representation.

The error message now generated is as expected