Dependency maintenance

[erwinkramer]

• dotnet to latest patch version
• mostly patch version updates for nuget packages, including Microsoft.Azure.DurableTask.Core to 3.7.1, exception is Grpc.Tools, which is a minor bump
• for github actions, everything to latest version
• removed the Microsoft.Azure.DurableTask.Core dependency for sample projects, not sure why it was there in the first place.
• completely dropped the Grpc.Core dependency. The Grpc.Core namespace is in other libraries as well now, or already has been for a while (via dependency Grpc.Net.ClientFactory and Grpc.AspNetCore.Server). Closes Replace Grpc.Core with superseded library #66.
• recently, a lot of documentation has been published on the base framework (Add comprehensive DTFx documentation Azure/durabletask#1299), i made sure to link that in the readme of this repo

Successfully tested the samples on .NET 10.

[lucaslorentz]

Looks good! Dependency updates are all reasonable (patch-level + Grpc.Tools minor bump). Dropping Grpc.Core is correct — the types (ServerCallContext, CallOptions, etc.) are already available through Grpc.AspNetCore.Server and Grpc.Net.ClientFactory. CI is green. Thanks for the thorough maintenance work!