[All] [.NET] Add .NET SDK support

[nalyd2]

SDK

All

Description

Add a .NET SDK (dotnet/) as a new wrapper language for the Zerobus Ingest SDK, providing high-throughput streaming ingestion into Databricks Delta tables for .NET applications.

Proposed Solution

A thin P/Invoke wrapper around the existing rust/ffi/ C ABI, following the same patterns as the Java SDK:

• Native interop: P/Invoke declarations, C struct marshaling, SafeHandle subclasses, cross-platform native library resolver
• Fluent builder API: StreamBuilder with typed sub-builders (.Json(), .CompiledProto(), .Arrow())
• Stream types: ZerobusJsonStream, ZerobusProtoStream<T>, ZerobusArrowStream (Beta) — all thread-safe
• Configuration: Builder pattern matching Java's StreamConfigurationOptions
• CI/CD: GitHub Actions workflows integrated into push.yml + release-dotnet.yml
• NuGet packaging: Multi-platform native libs bundled via runtimes/{rid}/native/
• Testing: 51 tests (30 unit + 21 integration with gRPC mock server)

The .NET SDK uses the same zerobus_ffi that Go and C++ consume — no new FFI crate required.

Additional Context

No response