BREAKING: Modularize client architecture, add Bulk API support

[tance77]

⚠️ Breaking Changes

This is a major refactor that restructures the crate's internals and changes the public API. It is not backwards compatible with the current release.

What breaks

• Response types removed: All typed response structs (QueryResponse, SearchResponse, DescribeResponse, etc.) have been removed. Methods now return serde_json::Value, giving consumers full flexibility to deserialize as needed.
• Module structure changed: src/client.rs and src/response.rs have been split into submodules. Anyone importing internals directly will need to update paths.
• Client constructor changed: Now takes client_id and client_secret directly, with setters for login URL, version, etc.
• Removed describe_global example (method still exists)
• Removed old integration tests — they depended on the deleted response types

What's new

• Modular architecture: Client split into client, rest_api, bulk_api, bulk_api_v2 submodules
• Bulk API v1 support: XML-based classic Bulk API (bulk_api module)
• Bulk API v2 support: CSV/JSON-based Bulk API v2 (bulk_api_v2 module)
• Dedicated response modules: token_response, token_error_response, error_response
• Access token module: Dedicated access_token module for token management
• Improved error handling: More granular error variants in errors.rs
• Updated dependencies: Bumped to edition 2021, updated all deps

Why

The original monolithic client.rs was difficult to extend. Typed response structs broke when Salesforce changed their API payloads. Returning generic JSON is more resilient and lets consumers define their own types if needed.

Test plan

• Verify existing examples compile and run against a Salesforce instance
• Test Bulk API v1 job creation, batching, and result retrieval
• Test Bulk API v2 job lifecycle
• Verify authentication flows (login, refresh token)

[tance77]

Adding Tooling API Support

[wimvelzeboer]

Hi @tance77 ,
I saw your PR while I was looking for a crate that integrates Rust and Salesforce, and I noticed that it looks like this repo is abandoned. With last updates from a year or two ago.
That is why I forked this repo and applied your changes there.
I also modified some methods (mostly what they return), using rust generics I was able to replace the Value of some return methods into specific responses.
What do you think of my changes? Rustsf crate

I plan to add support for the metadata api, which I require for my project.

Let me know what you think, maybe we can work together in getting rustforce to the next level.

[tance77]

@wimvelzeboer feel free to take the reins my times very limited when it comes to open source projects. Ill contribute from time to time but that's about it. I'm glad to see there are some active members out there wanting to see this one through.