vault: finalize request_id event encoding and fix revenue pool logic

[Kanasjnr]

Description

This PR addresses several critical issues in the callora-vault contract, focusing on event schema consistencynand achieving 100% test coverage.
Closes #115

Key Changes

• Event Schema Standardization: Implemented the mandatory 3-topic structure for deduct events. When request_id is not provided, an empty symbol ("") is now emitted as the third topic to ensure indexer stability.
• Revenue Pool Logic Fix: Corrected the logic in deduct and batch_deduct to properly verify and transfer USDC to the revenue_pool address set during initialization. Previously, the contract was incorrectly looking for a settlement key that was not yet configured.
• Storage Key Harmonization: Refactored internal state management to use the StorageKey enum across all functions, preventing runtime failures caused by inconsistent raw string keys.
• Test Suite Updates:
  • Updated all client.init calls to match the new 7-argument signature.
  • Added batch_deduct_events_contains_empty_request_id to verify the new event convention.
  • Fixed authorization in deduct_exceeds_balance_panics to ensure the balance check takes precedence over permission errors.
• Code Optimization: Removed unused imports (IntoVal), legacy constants (META_KEY, ALLOWED_KEY), and redundant balance checks in the deposit function.
• Documentation: Resolved merge conflicts in README.md and updated EVENT_SCHEMA.md and UPGRADE.md with the new event encoding standards.

Verification Results

All 59 tests in the callora-vault suite are passing:

cargo test -p callora-vault
# Result: 59 passed; 0 failed

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[Kanasjnr]

@greatest0fallt1me ready for review