Fix short raycasts missing large objects (#14339)

Increases the tolerance from one node to five nodes.
Also optimizes the "sphere" used for pre-filtering entities
to start in the middle of the line segment rather than at the start.

doc/lua_api.md

@@ -8403,6 +8403,8 @@ Player properties need to be saved manually.
     -- If `rotate = false`, the selection box will not rotate with the object itself, remaining fixed to the axes.
     -- If `rotate = true`, it will match the object's rotation and any attachment rotations.
     -- Raycasts use the selection box and object's rotation, but do *not* obey attachment rotations.
+    -- For server-side raycasts to work correctly,
+    -- the selection box should extend at most 5 units in each direction.
 
 
     pointable = true,

src/serverenvironment.cpp

@@ -1826,8 +1826,8 @@ void ServerEnvironment::getSelectedActiveObjects(
 	const std::optional<Pointabilities> &pointabilities)
 {
 	std::vector<ServerActiveObject *> objs;
-	getObjectsInsideRadius(objs, shootline_on_map.start,
-		shootline_on_map.getLength() + 10.0f, nullptr);
+	getObjectsInsideRadius(objs, shootline_on_map.getMiddle(),
+		0.5 * shootline_on_map.getLength() + 5 * BS, nullptr);
 	const v3f line_vector = shootline_on_map.getVector();
 
 	for (auto obj : objs) {