Feat: oracle consumer

[Agbasimere]

Closes: #23

Description

This PR implements the OracleConsumer module, enabling Soroban smart contracts to securely consume and cache data from external price oracles.

Features

• Data Standardization: Provides a common structure for asset pricing data (PriceData with price and timestamp).
• Staleness Logic: Built-in protection against outdated price feeds using configurable max_age checks.
• On-Demand Updates: update_price method pulls fresh data from a configurable external oracle address.
• Administrative Security: Authorized mechanisms to update the source oracle as needed.
• Event-Driven: Automated event emission for all price updates for downstream monitoring.

Integration

Located in src/oracle_consumer:

• Import as a crate via anchorpoint-oracle-consumer = { path = "../oracle_consumer" }.
• Initialize with an admin and an oracle address, then call update_price(asset) as needed before critical financial logic.

Commands

• Build/Check: cargo check -p anchorpoint-oracle-consumer
• Unit Tests: cargo test -p anchorpoint-oracle-consumer

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[Ceejaytech25]

@Agbasimere , lgtm!