rodbus-client modernization and rodbus-client hang fix

[nslee333]

This completes #151, and #155

• Update clap using V4's derive macro
• Add Serial support
• Migrate Box<Dyn std::error:Error>> to thiserror
• Extract magic numbers into constants

[gemini-code-assist]

Summary of Changes

Hello @nslee333, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly modernizes the rodbus-client application by upgrading its command-line interface to use clap v4's derive system, introducing support for Modbus RTU over serial connections, and enhancing error handling with the thiserror crate. These changes improve the client's usability, expand its capabilities, and make the codebase more maintainable.

Highlights

• Clap Upgrade & CLI Modernization: The command-line argument parsing for the rodbus-client has been completely rewritten. It now leverages clap v4's derive macros, making the CLI definition more declarative, robust, and easier to maintain. This includes defining top-level arguments, subcommands for TCP and Serial modes, and specific arguments for each Modbus command.
• Serial (Modbus RTU) Support: The client now supports connecting to Modbus devices over serial ports. A new serial subcommand has been added, allowing users to specify serial port path, baud rate, data bits, flow control, stop bits, and parity. This significantly expands the client's connectivity options beyond just TCP.
• Error Handling Improvement: The custom error handling mechanism has been replaced with the thiserror crate. This provides a more idiomatic and user-friendly way to define and propagate errors within the application, improving readability and maintainability of error types.
• Code Refactoring & Constants: Several 'magic numbers' have been extracted into named constants (CHANNEL_BUFFER_SIZE, REQUEST_TIMEOUT, MAX_QUEUED_REQUESTS), improving code clarity. The overall argument parsing logic has been simplified, and the ConnectionListener has been refactored into a generic StateListener.

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[gemini-code-assist]

Code Review

This pull request modernizes the rodbus-client with clap v4, derive macros, and thiserror for improved code clarity and maintainability. The addition of serial port support is a valuable new feature. The review focuses on connection state handling and error reporting.

[jadamcrain]

LGTM