[Rust] Send TransformSession options as JSON - #8658

Problem

The five Rust TransformSession constructors (new, new_with_mode, from_view, from_view_with_mode, from_context) take a &Settings and send settings.serialize_schema() as the session options. That string is the settings schema (groups, titles, types, defaults), not the values set on the instance. The core expects a JSON object of setting keys and values, which is what Python (json.dumps(options)) and the C++ default ("{}") send. The core ignores the schema, so per-session overrides such as files.container.excludedTransforms have no effect from Rust.

On dev, with a ZIP of two files and an override instance that excludes the Zip transform:

global: transform="Zip" children=2
override: transform="Zip" children=2

The override should give transform="" children=0.

Change

new, new_with_mode, from_view, from_view_with_mode and from_context now take options: Option<O> with O: IntoJson, like load_with_options. None sends {}. They return Option<Ref<TransformSession>>: None if the options can't be converted to JSON or the core returns no session, as load_with_options does. The doc of new describes the options format and has an example.

This is a breaking change. Callers pass None::<&str> or Some(json) instead of &settings and unwrap the result. The only caller in this repository, test_context_transform, is updated. I chose it over keeping &Settings because it matches load_with_options and the Python and C++ APIs. Keeping &Settings would need a wrapper for BNSerializeSettings (SettingsAutoScope), and per-session options would then have to live in a named Settings instance that is shared process-wide and carries values between sessions.

Testing

New rust/tests/transform_session.rs builds a two-file ZIP at test time, so there is no binary fixture. test_session_options checks that with None, new_with_mode and from_view_with_mode extract the ZIP (root transform Zip, 2 children), and that with {"files.container.excludedTransforms": ["Zip"]} they don't (no transform, 0 children). It passes on this branch.

The tests are in their own file because rust/tests/transform.rs registers MyDetectionTransform, which accepts any input of 4 bytes or more and would be applied to these sessions. On dev, running all of cargo test --test transform together already overflows the stack in test_context_transform for that reason; each test passes when run alone. This PR doesn't change that.

from_context sends the options too, but a session created from an existing context used that context's settings in my tests, so it isn't covered.

cargo fmt --check and cargo clippy -p binaryninja --all-features --lib --test transform --test transform_session are clean.