Fix MATLAB Eigen::Ref Jacobian output capture and overload dispatch

@thatdudegrantt This follows up on the Eigen `Ref` Jacobian-output work and [Copilot's review finding in GTSAM PR #2612](https://github.com/borglab/gtsam/pull/2612#discussion_r3681689465).

## Problem

The generated C++ MEX collector correctly writes the primary return value and Jacobians to `out[0]`, `out[1]`, etc., but the generated MATLAB `.m` stubs do not reliably expose those outputs.

Two related problems are present:

1. Jacobian overload calls capture only one MEX result:

```matlab
varargout{1} = (...);
```

This discards the additional Jacobian outputs. Instance and static method generation both need an LHS that captures all requested outputs, such as:

```matlab
[varargout{1:nargout}] = (...);
```

2. A non-Jacobian overload can appear first with the same non-`Ref` `varargin` signature. It has no `nargout` constraint, so it matches and returns before the later `nargout == N` Jacobian overload is reached.

For example, generated `transformFrom` dispatch currently has the ordinary one-argument overload before the one-argument-plus-`nargout == 3` Jacobian overload.

## Expected behavior

Calls such as:

```matlab
[result, Hself, Hpoint] = pose.transformFrom(point);
[result, H] = pose.inverse();
[result, Hxi] = gtsam.Pose3.Expmap(xi);
```

should select the Jacobian overload and return every MEX output.

## Suggested scope

- Generate a multi-output MATLAB LHS for Eigen `Ref` output overloads.
- Apply the behavior consistently to instance and static methods.
- Prioritize Jacobian overload dispatch or constrain the non-Jacobian sibling by `nargout`.
- Extend `test_eigen_ref_jacobians` to assert the generated `.m` assignment and ordering/selection, not only the `nargout` predicate and C++ `out[]` writes.

The existing focused test passes despite the broken generated MATLAB stub because those two properties are not currently asserted.