Migrate null annotations to jspecify

Currently, the sdk uses Reactor's reactor.util.annotation.Nullable annotations, such as here

https://github.com/modelcontextprotocol/java-sdk/blob/fd004989b9484c9b81be6b03463396797b354804/mcp-core/src/main/java/io/modelcontextprotocol/util/Assert.java#L28

This is causing warnings in my downstream build since that type refers to javax classes I don't have on the classpath.

This is Reactor Nullable, along with its imports:

import javax.annotation.Nonnull;
import javax.annotation.meta.TypeQualifierNickname;
import javax.annotation.meta.When;

@Nonnull(when = When.MAYBE)
@TypeQualifierNickname
@Deprecated
public @interface Nullable {
}

The Reactor type is now deprecated, and they recommend you using JSpecify which is fast becoming the standard, if it is not already.

I can possibly submit a PR for this, but I notice a lot of PRs opened recently have limited activity, so will wait for the go-ahead first.

Commencez par mcp-core/src/main/java/io/modelcontextprotocol/util/Assert.java et recherchez dans le dépôt reactor.util.annotation.Nullable ainsi que les annotations de nullité Reactor associées. Vérifiez la configuration du build pour la dépendance JSpecify, puis vérifiez que toutes les annotations pertinentes utilisent JSpecify et que le SDK se construit sans nécessiter les classes d’annotations javax.