C# implementation of Transactions for Procedures

[rekhoff]

Description of Changes

Implements the C# equivalent of #3638

This implement uses inheritance, where abstract base classes (like ProcedureContextBase in ProcedureContext.cs) store the core of the implementation, and then generated wrappers (like ProcedureContext in the generated FFI.cs file) inherit from them.

For error handling, we work like Rust's implementation of Result<T,E> but we require where E : Exception because of how exceptions work in C#. Transaction-level failures come back as a TxOutcome and user errors should follow the Result<T,E> pattern. In this implementation, we have UnwrapOrThrow() throws exceptions directly because of C#'s error handling pattern.

Unlike the Rust implementation's direct Result propagation, we are using an AbortGuard pattern (in ProcedureContext.cs) for exception handling, which uses IDisposable for automatic cleanup.

Most changes should have fairly similar Rust-equivalents beyond that.
For module authors, the changes here allow for the transation logic to work like:

ctx.TryWithTx<ResultType, Exception>(tx => {
    // transaction logic
    return Result<ResultType, Exception>.Ok(result);
});

This change includes a number of tests added to the sdks/csharp/examples~/regression-tests/'s server and client to validate the behavior of the changes. server changes provide further usage examples for module authors.

API and ABI breaking changes

Should not be a breaking change

Expected complexity level and risk

2

Testing

• Created Regression Tests that show transitions in procedures working in various ways, all of which pass.

[gefjon]

I'd like to see a more in-depth PR description which goes into detail on your design and implementation choices. Especially in big PRs like this, there's a burden on the author to both keep the changes as contained and laser-focused as possible, and also to proactively explain to reviewers what's going on in the diff. Anywhere I've left a comment asking for reasoning, that's the kind of thing that should be in your PR description proactively.

[JasonAtClockwork]

Looks solid now, I've run the regression tests and walked through the changes. One small nit would be to add Log.Debug() for all successful tests but I think we want to rework the test runner soon anyhow.

[gefjon]

This looks great, thanks!