Add batch claim functionality for multiple successful campaigns

[soma-enyi]

Closes #94

Batch Claim for Multiple Successful Campaigns

Allows claiming funds from multiple successful campaigns in a single transaction with safe
error handling.

Implementation:

• claim_campaign_funds() - Claims funds for a single successful campaign
• batch_claim_campaign_funds() - Processes multiple campaigns in one call
• Loop-based with isolated error handling - individual failures don't stop the batch
• Returns result vector showing success/failure for each campaign

Tests:

• ✅ Batch claim 3 successful campaigns
• ✅ Partial failures (2 succeed, 1 fails)
• ✅ Already-claimed detection
• ✅ Single claim validation
• ✅ Unsuccessful campaign rejection

Changes:

• Added claim functions to contract interface and implementation
• Added campaign_funds_claimed event
• Added CampaignClaimed storage key for double-claim prevention
• Comprehensive test suite in batch_claim_test.rs

[Akshola00]

@soma-enyi ci is failing

[Akshola00]

@soma-enyi test are failing

[Akshola00]

thanks fr your contribution