digiocean error propagation

[shivv23]

Summary

This PR removes panic-prone paths from DigitalOcean modules and propagates typed errors consistently.

Changes

• Updated DigitalOcean compute/dns/network/storage modules to return CloudError instead of relying on unwraps.
• Replaced JSON serialization unwraps with CloudError::Serialization.
• Replaced network/body read unwraps with CloudError::Network.
• Preserved existing response shape (status + body) for API compatibility.

Why

• Eliminates avoidable panics in provider operations.
• Makes failure handling consistent across provider implementations.

Validation

• cargo check --lib