Implement `donate` function

[ayshadogo]

User Story:
As a donor, I want to send tokens to the campaign contract so that my donation is recorded transparently on-chain.
Acceptance Criteria:

• fn donate(env: Env, donor: Address, amount: i128, asset: AssetInfo)
• donor.require_auth() called
• Validates: amount > 0, asset is accepted, campaign is active, deadline not passed
• Transfers tokens from donor to contract using Soroban token interface
• Updates raised_amount and DonorRecord
• Emits donation_received event with donor, amount, asset

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[Ajibose]

@Ajibose has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would love to take on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Ajibose to this issue.

[portableDD]

@portableDD has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Can i work on this?

ℹ️ Repo Maintainers: To accept this application, review their application or assign @portableDD to this issue.

[drips-wave]

Congratulations, @portableDD! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

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