feat(json-rpc-engine): Type-safe context inference

[rekmarks]

Explanation

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

---

Note

Introduce generic, type-safe MiddlewareContext and JsonRpcEngineV2.create() factory with improved type inference; update server, utils/exports, tests, and docs accordingly.

• Engine V2:
  • Add JsonRpcEngineV2.create() static factory; make constructor private and enforce non-empty middleware.
  • Enhance generics: middleware now typed with Context, ResultConstraint; improved request/notification typing and composition.
  • Support context-typed handle()/asMiddleware(); validate incompatible contexts at type level; new internal invalid-engine typing.
• MiddlewareContext:
  • Make MiddlewareContext generic with strict key/value typing; add assertGet/set typings, EmptyContext, and MergeContexts util.
• Utils/Types:
  • Re-export Json, JsonRpcParams; add UnionToIntersection type.
  • Extend JsonRpcEngineError with cross-version isInstance().
• Server:
  • Construct engine via create() when passed middleware; clarify/adjust param validation and id handling.
• Compatibility utils:
  • Type propagateToContext to accept typed context; minor param-handling tweaks.
• Tests:
  • Update to use create() and new helper middlewares; add coverage for context typing, invalid compositions, and new behaviors.
• Docs:
  • Rewrite/expand README examples for create(), typed middleware/context, composition patterns, and error semantics.

^{Written by Cursor Bugbot for commit 75f61e7. This will update automatically on new commits. Configure here.}

[mcmire]

Had one question about representing an invalid engine better, as well as some other comments. None of this is blocking though. I think this works really well.

[mcmire]

Nit: Would it be worth adding tsd or tstyche tests at some point for some of these classes? This would allow us to write assertions at the type level.

[rekmarks]

I think we're squeaking by with @ts-expect-error for now, although I'm not opposed to the idea if we think it becomes warranted.