Only use `TDBContextProxy`s for contexts from stack of the debugged process

[LinqLover]

For instance, when debugging the simulator, it can get a problem that every historic context is wrapped in a TDBContextProxy which does not account for changes in i.e. the method accessor.

Possible implementations:

• Introduce separate protocols in the cursor for retrieving TDBContextProxys, and only answer regular proxies via the normal interface.
• Before answering a context proxy, test whether there is a trace for the original object.
• Discuss what happens if the code is manipulating its contexts manually, and whether we want to support this.