Implement MilvusClientV2 (2.6)

[yhmo]

issue: #139

Summary

Adds MilvusClientV2, a new DTO-based Milvus client targeting the 2.6 API surface, alongside the existing V1 Milvus.Client. The client mirrors the V2 SDKs (Java / C++ / PyMilvus) with per-operation request/response DTOs, internal generated gRPC types, and the shared cache/retry infrastructure described in the design doc.

The milvus-proto submodule is upgraded to the 2.6 branch (a76db65) and relocated to the repository root, since it is now a shared build-time dependency of both the V1 and V2 assemblies. Neither published package references the protos at runtime.

What's included

Complete 2.6 API surface (Milvus.Client.V2)

• Collection & schema: create/drop/describe/alter, field & function operations, properties, replicas, truncate, refresh-load
• Index: create/drop/describe/list, index properties
• DML: insert / upsert / delete with Session-consistency timestamp tracking
• DQL: get / query / search / hybrid search (RRF & weighted rerankers) / query & search iterators
• Partition / database / alias
• RBAC: users, roles, privileges, v2 privilege model, privilege groups
• Resource group, utility (flush, compact, analyze, CDC / replicate info), bulk import

Mechanisms

• CollectionTsCache (Session read-your-writes) and single-flight SchemaCache, keyed by endpoint/database/collection
• RetryPolicy with the two-layer retryable-error decision (gRPC blacklist + server RateLimit), aligned with PyMilvus/Java/C++
• Server-streaming DumpMessages and lazy paged iterators

Quality & docs

• Three-layer test suite (Unit / Integration with in-process mock server / System against a real container)
• Runnable per-feature examples with doc headers and Snippet annotations
• BFloat16 vector support, nullable/JSON FieldData fixes, DropCollection cache invalidation

Compatibility

• V1 Milvus.Client is unchanged in behavior and remains buildable after the proto upgrade
• Both NuGet packages are unaffected by the submodule relocation (protos are a build-time-only input)

Test plan

dotnet test Milvus.Client.sln

• V2: 80/80 passing
• V1: 240 passing, 1 skipped

[mergify]

@yhmo Thanks for your contribution. Please submit with DCO, see the contributing guide https://github.com/milvus-io/milvus/blob/master/CONTRIBUTING.md#developer-certificate-of-origin-dco.

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[Copilot]

🔵 Needs a closer look

It introduces a large new client surface area plus core caching/endpoint normalization and request-shaping logic where multiple concrete correctness issues were found that should be addressed and re-validated.

Pull request overview

This PR introduces a new Milvus.Client.V2 SDK implementation targeting the Milvus 2.6 API surface (DTO-based request/response pattern with a single MilvusClientV2 facade), while keeping the existing V1 client buildable after relocating/upgrading the shared milvus-proto submodule.

Changes:

• Adds the new Milvus.Client.V2 library (DTO requests/responses, types, utilities like timestamp/schema caches and retry infrastructure).
• Adds a V2-focused test suite (unit/integration/system) and runnable examples showcasing V2 features.
• Relocates the milvus-proto submodule to the repo root and updates solution/package wiring to include V2 projects.

File summaries

File	Description
Milvus.Client/Milvus.Client.csproj	Updates protobuf include paths to reference protos from the new repo-root Protos location.
.gitmodules	Relocates the milvus-proto submodule entry to the repo root (Protos).
Directory.Packages.props	Adds centralized package versions needed for the new V2 test infrastructure.
Milvus.Client.sln	Adds the V2 library and V2 test projects to the solution.
Milvus.Client.V2/Utils/Verify.cs	Adds V2 argument validation helpers used across DTOs.
Milvus.Client.V2/Utils/TypeMappings.cs	Adds enum-to-wire-string mapping for index/search request parameters.
Milvus.Client.V2/Utils/MilvusTimestampUtils.cs	Adds timestamp conversion helpers for guarantee/time-travel timestamps.
Milvus.Client.V2/Utils/Logging.cs	Adds source-generated logging extension methods for V2 client operations.
Milvus.Client.V2/Utils/CompilerAttributes.cs	Adds internal compatibility attributes for older target frameworks.
Milvus.Client.V2/Utils/CollectionCacheKey.cs	Adds cache key normalization for schema/TS caches keyed by endpoint/db/collection.
Milvus.Client.V2/Types/*	Introduces public V2 types/enums supporting the 2.6 API surface (metrics, load/index states, iterators, retry config, replication models, etc.).
Milvus.Client.V2/Requests/*	Adds DTO request objects for V2 operations (collection/index/DML/DQL/utility/RBAC/etc.).
Milvus.Client.V2/Responses/*	Adds DTO response objects for V2 operations.
Milvus.Client.V2/MilvusException.cs	Adds V2 exception type carrying MilvusErrorCode.
Milvus.Client.V2/MilvusErrorCode.cs	Adds V2 error code enum.
Milvus.Client.V2/MilvusClientV2.BulkImport.cs	Adds Bulk Import facade methods wired to DTOs and gRPC calls.
Milvus.Client.V2.Tests/Milvus.Client.V2.Tests.csproj	Adds the V2 test project and its dependencies.
Milvus.Client.V2.Tests/Unit/*	Adds unit tests for V2 utilities and request mapping logic.
Milvus.Client.V2.Tests/Integration/*	Adds integration tests using an in-process mock server to validate client behavior.
Milvus.Client.V2.Tests/System/*	Adds system tests against a real Milvus container.
examples/Milvus.Examples.csproj	Adds runnable examples project referencing Milvus.Client.V2.
examples/Program.cs	Adds an example runner/dispatcher for V2 examples.
examples/*Example.cs	Adds runnable V2 examples demonstrating specific features (RBAC, analyzer, aliases, nullable fields, etc.).
examples/ExampleHelpers.cs	Adds shared helper utilities for making examples idempotent and easy to run.

Review details

• Files reviewed: 271/272 changed files
• Comments generated: 8
• Review effort level: Lite

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[mergify]

@yhmo Thanks for your contribution. Please submit with DCO, see the contributing guide https://github.com/milvus-io/milvus/blob/master/CONTRIBUTING.md#developer-certificate-of-origin-dco.