feat:implimented TTL configuration

[Agbeleshe]

Summary

This PR implements storage optimization strategies for the escrow contract by introducing Time-To-Live (TTL) management and data archiving mechanisms. The goal is to reduce on-chain storage footprint and minimize long-term costs for users in line with Soroban best practices.

Changes Made

• Added TTL configuration for escrow records (default: 6 months)
• Implemented an extend_ttl function to allow extension of active escrows
• Introduced cleanup logic to remove expired or refunded escrow data
• Ensured storage deposits are reclaimed where applicable
• Updated internal storage handling to maintain a lean contract state

Technical Details

• TTL is applied at the time of escrow creation
• extend_ttl can only be called on active escrows
• Cleanup function safely deletes expired or finalized records
• Logic ensures no valid or active escrow data is accidentally removed

Testing

• Verified TTL is correctly set and extended
• Tested cleanup function for expired and refunded escrows
• Confirmed no impact on active escrow operations
• Ensured storage usage is reduced after cleanup execution

Notes

This implementation follows Soroban storage best practices to optimize contract efficiency and reduce unnecessary storage costs over time.

Closes: #159

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[Cedarich]

@Agbeleshe please fix workflow

[Agbeleshe]

@Cedarich please review

[Agbeleshe]

@Cedarich please review

[Agbeleshe]

@Cedarich awaiting review

[Cedarich]

@Agbeleshe please fix clippy

[Agbeleshe]

@Cedarich Please review

[Cedarich]

LGTM