[2.0 Breaking]: Remove sender field from [Reducer|View|Procedure]Context

[joshua-spacetime]

Description of Changes

Makes the sender field on ViewContext private and exposes a sender() method. Does the same for ReducerContext and ProcedureContext.

The purpose of this change: So that the host can determine if/when a view invokes or reads the sender.

Currently, because sender is a field, the host assumes that it is always read. This means views must be materialized per client, even if the view doesn't actually depend on sender, resulting in data duplication.

The initial solution for this problem was AnonymousViewContext which doesn't have a sender field. The better solution is to make sender a method so that it can call into the host and record when it's actually invoked.

Note, this patch only updates the module API, so the current implementation does not change. ViewContext views are still duplicated across clients. Changing this requires a new host syscall and for sender() to invoke that syscall. This however is backwards compatible and can be done anytime after the module APIs for the other languages (C#, TypeScript, C++) are updated.

Also note that ReducerContext and ProcedureContext were updated purely for consistency. There are currently no plans to track reads of sender in these contexts.

API and ABI breaking changes

Breaks the rust module api.

Expected complexity level and risk

1

Testing

N/A