fix: serviceability: return InvalidPublicIp for device public IP validation

[nikw9944]

Summary

• Fix Device::validate() to return InvalidPublicIp (variant 62) instead of InvalidClientIp (variant 26) when the device public IP fails the is_global() check
• Update Go SDK error formatter test to use the correct error code so the test example is coherent

The bug caused the CLI to display "Invalid Client IP" when the program log said "Invalid public IP":

❯ doublezero device update --pubkey 4CkvmyquGN4qtXLNj3hpJcqYbb7PCanLbU1rQHHdp6xp --status drained
Program Logs:
Program GYhQDKuESrasNZGyhMJhGYFtbzNijYhcrN9poSqCQVah invoke [1]
Program log: Instruction: UpdateDevice(status: Some(Drained), resource_count: 0, )
Program log: Invalid public IP: 0.1.2.3
Program GYhQDKuESrasNZGyhMJhGYFtbzNijYhcrN9poSqCQVah consumed 8544 of 200000 compute units
Program GYhQDKuESrasNZGyhMJhGYFtbzNijYhcrN9poSqCQVah failed: custom program error: 0x1a
Error: Invalid Client IP

After this fix, the CLI will display "Invalid Public IP: IP conflicts with DZ prefix" which matches the InvalidPublicIp variant's error message.

[nikw9944]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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