cosmos: add experimental c wrapper around cosmos sdk

[analogrelay]

This is a bit of an experiment, but I'm game to merge it if @heaths and other Cosmos folks like it.

We want to explore the option of publishing a C library of the Azure Cosmos DB SDK for Rust. This PR adds the basic framework to start that effort:

• A new package cosmosclient that depends on azure_data_cosmos. This package builds a cdylib and staticlib target (libcosmosclient.a/libcosmosclient.so/cosmosclient.dll/etc.) that exports a C-compatible API. For now, that API is extremely simple (cosmosclient_version).
• A simple test infrastructure (NOT currently integrated into anything). There are C programs in sdk/cosmos/cosmosclient/c_tests that will be built and linked against the cosmosclient library. The tests are simple pass/fail programs. If the test returns a 0 exit code, it passed, otherwise, it failed.
• build.rs script in cosmosclient to produce sdk/cosmos/cosmosclient/include/cosmosclient.h, which is a C header file defining the API surface of cosmosclient. We should publish this as an artifact at some point, but for now it's there to be used by tests.

[Copilot]

Pull Request Overview

This PR adds an experimental C wrapper around the Azure Cosmos DB SDK for Rust, introducing a new cosmosclient package that exports a C-compatible API. The goal is to explore publishing a C library version of the Cosmos DB SDK.

Key changes:

• New cosmosclient crate that builds both static and dynamic C libraries
• C header generation using cbindgen with version information
• Basic C test infrastructure using CMake for validation

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
sdk/cosmos/cosmosclient/src/lib.rs	Core library implementation with C-compatible API and version function
sdk/cosmos/cosmosclient/Cargo.toml	Package configuration for building C libraries (cdylib/staticlib)
sdk/cosmos/cosmosclient/build.rs	Build script for generating C headers and build identifiers
sdk/cosmos/cosmosclient/CMakeLists.txt	CMake configuration for C test compilation and linking
sdk/cosmos/cosmosclient/c_tests/version.c	C test program to validate version consistency
sdk/cosmos/azure_data_cosmos/Cargo.toml	Added "c" feature for exposing additional types to C wrapper
Cargo.toml	Added cosmosclient to workspace members

[LarryOsterman]

Just two minor nits.

[analogrelay]

/azp run rust - pullrequest

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[heaths]

The vcpkg issue should be fixed now after #3076 but you also have a problem the Analyze step found:

Caused by:
  failed to parse manifest at `/mnt/vss/_work/1/s/sdk/cosmos/azure_data_cosmos_native/Cargo.toml`

Caused by:
  error inheriting `cbindgen` from workspace root manifest's `workspace.dependencies.cbindgen`

Caused by:
  `dependency.cbindgen` was not found in `workspace.dependencies`

[heaths]

/azp run rust - pullrequest

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[heaths]

You'll need to rebase again. There was some breaking change in eng/common that went in and is fixed for JS and Rust. That said, there are still some analysis errors. I'm also concerned that you use a specific version in build-dependencies and should've been flagged. We generally don't allow that in eng/scripts/verify-dependencies.rs. We catch those normally. I'd rather make sure all versions are consistent at time of release.