Add safe fallback to decodeMessage to prevent crashes on invalid bytes32

[anim001k]

Description

Fixes a potential crash in @semaphore-protocol/utils when decodeMessage receives non-string bytes32 values (like addresses, hashes, or arbitrary uint256).

Problem

The decodeBytes32String function in ethers v6 throws an exception when attempting to decode invalid UTF-8 sequences or non-string bytes32 values. This could cause UI/CLI applications to crash unexpectedly.

Solution

• Added try-catch wrapper around decodeBytes32String call
• Returns hex representation as fallback when decoding fails
• Maintains backward compatibility for valid string inputs
• Added test coverage for invalid bytes32 handling