grate with netframework 4.6+

Hi all.

The industry is moving away from netframework, however, we will still have a dozen legacy projects in production running .net framework 4.6+.
Developing the integration tests in .net fx is a real pain in almost cases, since docker and testcontainers defacto way of testing, I wonder any possible to convert grate to support .netstandard2.0 along side with modern .net10+.
To make it fully compatible with netstandard2.0, we will need
+ Add the Polyfills (PolySharp) as a compat layer, which supports new C# syntax while the source code compiles in .netstandard and .net
+ If the API doesn't exist in netstandard2.0, we will need a conditional #if NETSTANDARD2_0 code path or a helper.
+ Suggest moving only the `grate.*` library, `

Happy to discuss in detail, please leave your thoughts.

Thanks.

Start by reviewing the `grate.*` library project and its current target frameworks, then inspect the integration-test setup that currently depends on Docker and Testcontainers. Determine the APIs requiring PolySharp or conditional `NETSTANDARD2_0` paths; done means the library builds for netstandard2.0 alongside modern .NET 10+ and its integration tests remain usable.

Written by the indexing model from the issue text.