API vocabulary: MethodInfo spelled out, sessionId everywhere, legacy registration obsolete

[Astn]

Implements the API vocabulary decisions in AUS-986, reached in a debate on the naming of "method" and "session" and accepted by both sides. Before 2.0.0 final; no aliases for preview names.

The rule

"method" is always the JSON-RPC callable named on the wire; a MethodInfo is always spelled MethodInfo; the CLR side of a method is its implementation (a delegate, or a [JsonRpcMethod] member of a class or interface); a "service" is an object or type whose members become methods. A "session" is a named set of methods with its own configuration. ServiceBinder.BindMethod and UnbindMethod keep their names.

Code

• RpcMethod.FromMethod (three overloads) is RpcMethod.FromMethodInfo; FromDelegate is unchanged.
• RpcInterfaceMethod.Method is RpcInterfaceMethod.MethodInfo. This removes "inspect m.Method" on an RpcInterfaceMethod from the README, the double meaning the rule exists to remove.
• Handler.RegisterFuction and UnRegisterFunction keep their names and behaviour and are [Obsolete]; the message on the first says that BindMethod throws on a duplicate name where RegisterFuction replaces it. Tests that exercise the legacy pair suppress CS0618 locally.
• The session parameter is spelled sessionId on every overload; BindService, Handler.RegisterInstance and the JsonRpcService(string) constructor used sessionID. Only a named argument sessionID: breaks; the tree has none.
• Handler gets a class summary; JsonRpcOptions.SessionSelector's summary says the selection is independent of ASP.NET Core session state.

Documentation

• README "Defining methods" opens with a definition of method that says ServiceBinder never asks for a MethodInfo; the Delegates lead sentence is rewritten; "Sessions and context" opens with a definition of session.
• The package README gets the one-sentence definition of a method after the Getting started service step.
• CHANGELOG "Changed" and docs/upgrading.md "Changes that break the build" record the two renames and the spelling change.

Verification

• dotnet build AustinHarris.JsonRpc.sln -c Release: 0 errors.
• dotnet test AustinHarris.JsonRpcTestN -c Release: 1,191 passed on net8.0 and 1,191 on net10.0, 0 failed.
• site/build.py, render.py --check and test_render.py pass; no benchmark figure changed.