Client refactoring

[Satyam709]

This pull request introduces a major refactor and redesign of the DFS client, replacing the previous CLI and internal structure with a new, modular, and production-ready SDK (dfsclient). The CLI is now a thin wrapper over this SDK and supports robust commands for uploading, downloading, listing, and deleting files. The previous monolithic and manually-wired approach is replaced by a clean, extensible API with clear separation between public and internal code.

The most important changes are:

SDK Redesign and Public API (dfsclient):

• Introduced the new dfsclient package, which provides a clean, public SDK for interacting with the distributed file system, including types for progress reporting, upload/download results, and file info. All internal logic is hidden behind this façade. [1] [2]
• Added flexible configuration via functional options (e.g., WithMetadataAddrs, WithChunkSize, etc.), enabling easy customization and environment overrides.

CLI Overhaul:

• Replaced the old CLI in client/cmd/main.go with a new CLI in client/cmd/dfs-cli/main.go that is a thin wrapper over the dfsclient SDK, supporting upload, download, list, and delete commands with user-friendly output and progress reporting. [1] [2]

Internal Structure and Configuration:

• Moved all internal configuration and implementation details into client/internal packages, ensuring a clear separation between public API and internal logic. The old client/config.go is replaced by client/internal/dfsclientconfig.

Removal of Legacy Code:

• Deleted the previous CLI and configuration files (client/cmd/main.go, client/config.go) that were tightly coupled and less flexible, in favor of the new modular approach. [1] [2]

This refactor provides a modern, maintainable, and extensible foundation for the DFS client, making it easier to use both as a CLI and as a library in other Go programs.