[TASK-383] Error Handling fix CPP, for pointer returning methods

[fresh-borzoni]

Summary

closes #383

Replaces CXX Result<*mut T> bridge signatures with FfiPtrResult struct to preserve server error codes that were previously lost when CXX converted Rust errors into rust::Error (string-only)

[fresh-borzoni]

@luoyuxia @zhaohaidao @leekeiabstraction PTAL 🙏

[Copilot]

Pull request overview

This PR updates the C++ ↔ Rust CXX bridge for pointer-returning APIs to preserve server-side error codes by returning an intermediate FfiPtrResult (instead of Result<*mut T> which collapses errors to string-only rust::Error).

Changes:

• Introduces FfiPtrResult { result: FfiResult, ptr: ... } in the Rust CXX bridge and updates pointer-returning Rust APIs to use it.
• Updates C++ wrappers (connection/table/writer creation + write calls) to decode FfiResult and extract the returned pointer on success.
• Adjusts WriteResult destruction to use an explicit Rust-side deleter (delete_write_result).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
bindings/cpp/src/lib.rs	Adds FfiPtrResult, helper constructors, updates multiple Rust FFI exports to return it, and adds delete_write_result.
bindings/cpp/src/connection.cpp	Switches connection/admin/table getters to consume FfiPtrResult and preserve error codes.
bindings/cpp/src/table.cpp	Switches writer/scanner/lookuper creation and write calls to consume FfiPtrResult; updates WriteResult drop path.
bindings/cpp/src/ffi_converter.hpp	Adds ptr_from_ffi helper to convert FfiPtrResult.ptr to typed pointers.

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[fresh-borzoni]

Addressed comments

[leekeiabstraction]

TY for the PR, left a comment. PTAL

[fresh-borzoni]

@leekeiabstraction Ty for the review
Answered comment, PTAL 🙏

[luoyuxia]

@fresh-borzoni Thanks. Merging..