Update to .NET 10 and latest NuGet packages

[Copilot]

Upgrades all projects from netstandard2.0/netcoreapp2.2/netcoreapp3.1 to net10.0 and bumps all NuGet dependencies to current stable releases.

Package versions

Package	Before	After
MessagePack	2.1.90 / 2.5.187	3.1.4
RestSharp	106.12.0	114.0.0
NUnit	3.12.0	4.5.1
NUnit3TestAdapter	3.15.1	6.2.0
Microsoft.NET.Test.Sdk	16.4.0	18.3.0
Moq	4.14.5	4.20.72
RangeTree	2.0.1	3.0.1
MessagePackAnalyzer	2.1.165	3.1.4

Breaking change fixes

RestSharp 107+ API changes

• Method.GET → Method.Get (PascalCase enum)
• client.Execute(request) now requires using RestSharp; (moved to extension method)
• client.BaseHost = url removed — base URL passed to constructor instead
• Removed callback-based ExecuteAsync(request, callback) in favour of fire-and-forget _ = client.ExecuteAsync(request)
• new RestRequest(Method.Get) (no resource path) → new RestRequest()

RangeTree 3.x renamed to IntervalTree

// Before
using RangeTree;
public RangeTree<int, EntityId> Buckets = new RangeTree<int, EntityId>();

// After
using IntervalTree;
public IntervalTree<int, EntityId> Buckets = new IntervalTree<int, EntityId>();

NUnit 4.x

• CollectionAssert.AreEqual(expected, actual) → Assert.That(actual, Is.EqualTo(expected))

MessagePack 3.x source generator
The project uses TypelessContractlessStandardResolverAllowPrivate which doesn't require [MessagePackObject]/[Key] attributes; the stricter 3.x analyzer diagnostics (MsgPack003/004/005/007/011) are suppressed via <NoWarn> in each project. Two generator-breaking issues required code changes:

• Added parameterless constructor to CreateGroupChat.Params (source generator requires it)
• Made LocalChatMessage partial (required for types with private serializable members)

Other

• Removed stale <OutputType>Exe</OutputType> from dev.csproj — the Main entry point has been commented out for some time