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

[dellaert]

@thatdudegrantt This follows up on the Eigen Ref<MatrixXd> Jacobian-output work and Copilot's review finding in GTSAM PR #2612.

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:

   varargout{1} = <mex>(...);

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

   [varargout{1:nargout}] = <mex>(...);

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:

[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.