Implement secure randomBytes function with error handling

[zendrx]

Summary

This PR adds a randomBytes function to the crypto standard library module, providing cryptographically secure random byte generation.

Changes

• src/lib/crypto.buzz: Added randomBytes(len: int) > str declaration
• src/lib/buzz_crypto.zig: Implemented randomBytes using std.Io.random

API

/// Generate cryptographically secure random bytes
/// @param len Number of random bytes to generate
/// @return Random bytes as a string
export extern fun randomBytes(len: int) > str;

[giann]

This also needs some tests

[zendrx]

Have been able to resolve some requested changes