Optimize Group::select() with short-circuit checks before positionEdgeVariables()

[Copilot]

Canvas::itemAt() hit-tests every group via clickType() → select(), which unconditionally called positionEdgeVariables() — an expensive operation invoking margins() (Pango bounding-box updates) and moveTo() on every edge variable, even for groups nowhere near the click point.

Changes

• Empty-list short-circuit: return nullptr immediately when both inVariables and outVariables are empty — zero overhead for groups with no edge variables.
• Bounds short-circuit: skip positionEdgeVariables() when (x,y) is outside a conservative AABB centered on the group. Uses maxExtent = w + h as the half-extent, which is a tight upper bound for any rotation angle (for half-dims w, h, the rotated AABB half-dim satisfies w|cosθ| + h|sinθ| ≤ w + h).

// Short-circuit: no edge variables to hit-test.
if (inVariables.empty() && outVariables.empty())
  return nullptr;

// Short-circuit: skip expensive positionEdgeVariables() when clearly outside bounds.
const float z = zoomFactor();
const float w = 0.5f * iWidth() * z;
const float h = 0.5f * iHeight() * z + topMargin * z;
const float maxExtent = w + h;
if (abs(x - this->x()) > maxExtent || abs(y - this->y()) > maxExtent)
  return nullptr;

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This change is 

[Copilot]

Pull request overview

This PR optimizes canvas hit-testing by reducing unnecessary work in Group::select() during Canvas::itemAt() calls, avoiding expensive edge-variable positioning/layout in common “miss” cases.

Changes:

• Add an early return when both inVariables and outVariables are empty.
• Add a bounding-box-based early return to skip positionEdgeVariables() when the click point is clearly outside a conservative extent.

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[Copilot]

The new AABB short-circuit uses only the group icon dims (iWidth/iHeight + topMargin) to decide whether to skip positionEdgeVariables(). However edge variables can be laid out well outside those bounds (eg yOff grows with the number/height of in/out variables in layoutEdgeVariables), so this can return nullptr even when (x,y) is actually over a drawn edge variable/port, breaking hit-testing/wire dragging for groups with many edge vars (and potentially large label extents/margins). Consider widening the bound using a conservative upper bound that includes possible edge-variable extents (eg based on counts and cached bb heights/widths), caching margins/edge-extents from the last layout, or removing this short-circuit if correctness can’t be guaranteed.

Suggested change

	// Short-circuit: avoid the expensive positionEdgeVariables() call when
	// (x,y) is clearly outside the expanded group bounding box. Using
	// w+h as the conservative AABB half-extent covers all rotation angles.
	const float z = zoomFactor();
	const float w = 0.5f * iWidth() * z;
	const float h = 0.5f * iHeight() * z + topMargin * z;
	const float maxExtent = w + h;
	if (abs(x - this->x()) > maxExtent || abs(y - this->y()) > maxExtent)
	return nullptr;