feat: Implement Transaction, Transfer, Banking, and Direct Charge APIs

[YabetsZ]

Pull Request

Short description

• What: Implements support for 12 new official API endpoints across four core domains: Transactions, Transfers, Banking, and Direct Charges.
• Why: To achieve near-complete SDK coverage of the official documentation and enhance utility for complex payment flows (e.g., transfers, direct charges).
• How:
  Here are the list of things changed:
  • Documentation was revised to reflect the new feature set and generated API items.
  • Initial work for the encryption feature is underway, though it remains fully unimplemented in this PR.
  • The utils feature flag is finished, including the transaction reference generator functionality.
  • New Modules and 14 Endpoints Added:
    • The bulk of this work covers creating models, integration tests, and examples for all new endpoints.

Checklist

• PR targets the correct branch
• Code compiles without errors
• Tests added/updated or not applicable
• CI passes
• Docs/CHANGELOG updated if needed
• PR follows Conventional Commits (feat:, fix:, docs:, etc.)

Testing

• Run: make check
• Notes: Running make check will execute the extensive suite of newly added test cases covering all endpoints.
  @isrugeek

---

Note

Implements new Banking, Transactions, Transfers, and Direct Charge APIs with models, tests, examples, plus utils (tx_ref), feature flags, and docs/config updates.

• Core API (client):
  • Add endpoints: banks, balances, balances/{currency}, swap; transaction/initialize, transaction/verify/{tx_ref}, transactions, transaction/events/{tx_ref}; transfers (initiate), transfers/verify/{reference}, bulk-transfers, transfers?batch_id=..., transfers (list); charges?type=..., validate?type=....
• Models & Responses:
  • New/expanded models: bank::{BalanceData, SwapOptions, SwapData}, payment::{VerifyPaymentData, TransactionLog, GetTransactionsData, Transaction, Pagination}, direct_charge::{DirectChargeType, DirectChargeOptions, VerifyDirectChargeOption, DirectChargeData}, transfer::{TransferOptions, VerifyTransferData, BulkTransferOptions, BulkData, BulkTransferData, TransfersData, TransferMeta}.
  • Generic response types: ChapaResponse, ChapaResponseWithMeta; add DirectChargeVerifyResponse.
  • Remove legacy models/transaction.rs (consolidated into payment.rs).
• Config & Error:
  • ChapaConfig gains optional encryption support (feature-gated), builder env defaults; fields made crate-visible; add MissingEncryptionKey; add JsonError.
• Utils & Features:
  • Add utils module with generate_tx_ref (feature utils).
  • Scaffold chapa_encrypt::encrypt_data behind encryption feature (unimplemented).
• Examples & Tests:
  • Add examples for balances, transactions/logs, transfers (single/bulk), swap, tx_ref generation.
  • Extensive integration tests for all new endpoints using mockito.
• Project setup:
  • Crate name normalized to chapa_rust; add optional deps (des, base64, rand) and feature flags; .env.example adds ENCRYPTION_KEY; makefile docs with --all-features; README updated.

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