fix: remove dead storage helpers in campaign/src/storage.rs (#80)

[Xhristin3]

Summary

Three pub helpers in campaign/src/storage.rs were defined but never called from any contract entrypoint or referenced outside their own definitions: bump_all_persistent, get_contract_status, and set_contract_status. The DataKey::ContractStatus variant existed solely to back the latter two. Removed all dead code to reduce maintenance surface and eliminate unreachable public API.

Changes

• Removed get_contract_status and set_contract_status from campaign/src/storage.rs
• Removed bump_all_persistent from campaign/src/storage.rs
• Removed DataKey::ContractStatus variant from campaign/src/types.rs

Testing

Existing campaign contract tests pass without modification — the change is pure dead code removal with no behavioural impact.

Closes #80