feat: Add payment history command to CLI and update bill history description

[danieyal]

This pull request adds a new payment-history CLI command, clarifies the distinction between bill and payment history in both the CLI and documentation, and updates the data model documentation to include new types. These changes improve clarity for users and provide access to more detailed billing and payment information.

CLI Improvements

• Added a new payment-history command to the CLI, which retrieves and displays both bill and payment history for a given account, with support for JSON output.
• Updated the bill-history command and its help text to clarify that it only returns bills issued, not payments.

Documentation Updates

• Updated the CLI usage examples in README.md to clarify the difference between bill-history (bills issued) and payment-history (bills and payments), and to reflect the new command.
• Expanded the code example in README.md to show how to fetch both bill and payment history, and added a note about passing CustomerAccount objects to methods.

Data Model Documentation

• Added BillHistoryEntry, PaymentHistoryEntry, and AccountDueAmount to the documented data models in README.md to reflect new response types.

[Copilot]

Pull request overview

Adds a new CLI command to fetch combined bill+payment history, and updates user-facing docs to clearly distinguish “bill history” (bills issued) from “payment history” (bills and payments).

Changes:

• Added payment-history CLI command that calls get_payment_history() and renders a combined history table (with JSON output support).
• Updated bill-history CLI description/help to clarify it returns bills issued (not payments).
• Updated README.md CLI examples and documented data models to include the new history entry types.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/mytnb/cli.py	Adds payment-history command and clarifies bill-history help text.
README.md	Updates examples/CLI usage text and expands the documented data models for the new response types.

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