`AssetInfo` struct and status enums

[ayshadogo]

User Story: As a developer, I want a reusable asset representation and explicit status enums so that multi-asset support and state transitions are consistent and auditable.

Acceptance Criteria:

• AssetInfo: asset_code: String, issuer: Option<Address> (None for XLM), with an is_xlm() helper; validated at initialization
• CampaignStatus: Active, GoalReached, Ended, Cancelled; MilestoneStatus: Locked, Unlocked, Released — both derive contracttype
• Doc comments on each enum stating which transitions are valid; invalid transitions elsewhere in the contract must panic with a descriptive error (wire the check where the mutation actually happens, document the rule here)

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[OpensrcLord]

Hello @maintainer, I’ve gone through the requirements and I’m confident I can implement a proper solution that matches the acceptance criteria. Kindly assign this issue to me. And I will deliver at the shortest possible time.

[AnnieIj]

Hi! I'd love to work on this issue.

I plan to implement the AssetInfo struct and the associated status enums, ensuring they integrate cleanly with the existing data model and project architecture. I'll define clear, maintainable types, add the necessary validation and tests, and update any relevant documentation to reflect the new structures. Could you please assign this issue to me?

[OAKVISUALZ]

Please assign me this issue.