Enable pushing RigidConstraint objects to GSA

[Copilot]

RigidConstraint had a working ToGsaString converter emitting RIGID.2, but pushing always produced a "not supported" warning because the type was absent from the ToGsaString(this Type type) routing table in _ToGsa.cs, causing dispatch to fall through to the generic fallback.

Change

• GSA_Adapter/Convert/ToGsa/_ToGsa.cs — added RigidConstraint → "RIGID" to the type-routing method alongside the existing RigidLink entry:

else if (type == typeof(RigidLink))
    return "EL";
else if (type == typeof(RigidConstraint))   // added
    return "RIGID";
else if (type == typeof(LinkConstraint))
    return "PROP_LINK";

No new using was required; BH.oM.Adapters.GSA.Elements was already imported. The existing ToGsaString(this RigidConstraint rigidConstraint) converter is now correctly reached via dynamic dispatch.

[staintono]

@copilot Verify that this conforms to the BHoM standards and methods for PRs and the code

[Copilot]

@copilot Verify that this conforms to the BHoM standards and methods for PRs and the code

The change conforms to BHoM standards:

• Code style: The new else if branch follows the identical pattern used for every other type in ToGsaString(this Type type) — same indentation, same brace-free single-line style, placed logically alongside RigidLink.
• No new using needed: BH.oM.Adapters.GSA.Elements (which contains RigidConstraint) was already imported in the file.
• No [Description]/[Input]/[Output] attributes needed: The ToGsaString(this Type type) method has no such attributes (unlike some other methods in the file), consistent with all other entries in that switch-style block.
• Minimal change: Only the single missing routing case is added; nothing else is touched.
• Existing converter untouched: ToGsaString(this RigidConstraint rigidConstraint) in Elements/RigidConstraint.cs is called correctly via dynamic dispatch once the type is routed.

The change is purely additive and targeted, which is the BHoM expectation for this kind of fix.