feat(freeze,revenue_pool): connect freeze flag to revenue pool distributions (#1218)

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Closes #1218

Summary

Connects CalloraFreeze to RevenuePool distributions via an optional configured cross-contract circuit-breaker check:

1. Adds set_freeze_contract(env, caller, Option<Address>) and get_freeze_contract(env) on RevenuePool.
2. Consults is_frozen on the configured CalloraFreeze contract inside RevenuePool::require_not_paused and RevenuePool::is_paused, blocking distribute and batch_distribute with RevenuePoolError::Paused while frozen.
3. Preserves existing standalone behaviour when no freeze contract is configured (None).
4. Documents the integration model in contracts/freeze/README.md and adds end-to-end cross-contract integration tests in contracts/freeze/tests/malformed_freeze.rs.

Acceptance Criteria Mapping

• Freezing blocks revenue pool distribute when wired: Verified in freeze_contract_blocks_revenue_pool_distribute_when_wired.
• Unconfigured freeze address keeps current behaviour: Verified before wiring (pool.get_freeze_contract() == None).
• Integration test covers the cross-contract flow: Added freeze_contract_blocks_revenue_pool_distribute_when_wired in contracts/freeze/tests/malformed_freeze.rs.
• Freeze crate README states the integration model: Added the Revenue Pool Integration Model section in contracts/freeze/README.md.

Validation

• cargo test -p callora-freeze && cargo test -p callora-revenue-pool

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Payout Wallet (Base Mainnet USDC / EVM): 0x3806cd592a508d1992Ed007C2F53de251C2E7452