Codegen silently ignores explicit enum discriminant values

[clockwork-labs-bot]

Problem

When a Rust module defines an enum with explicit discriminant values:

#[derive(SpacetimeType)]
enum MyEnum {
    A = 1,
    B = 2,
    C = 3,
}

SATS encoding assigns variant tags by declaration order (0, 1, 2), completely ignoring the Rust discriminant values (1, 2, 3). Client-side codegen then generates enums with the SATS tag order, resulting in a mismatch between server and client enum values.

This means the server thinks A = 1 but the client thinks A = 0, silently corrupting data when enum values are used for anything beyond pattern matching.

Expected Behavior

The derive macro should emit a compile error when explicit discriminant values are used, since they cannot be preserved through the SATS encoding.