Change the type of LogContext

We don’t actually emit any context at the moment, I believe, nor do we
tell users what they’re meant to do with it. But, still, before our
first release of the public API, let’s use a type that the user can at
least easily pass through to a logging backend.

We still have #8 for figuring out what this context is actually meant to
be used for.

Sources/AblyChat/Logging.swift

@@ -1,6 +1,6 @@
 import os
 
-public typealias LogContext = [String: any Sendable]
+public typealias LogContext = [String: JSONValue]
 
 public protocol LogHandler: AnyObject, Sendable {
     /**