sci-mathematics/manifold: crank subslot for broken ABI

zen_desu reported openscad not opening:
```
$ openscad
openscad: symbol lookup error: openscad: undefined symbol: _ZN8manifold11TriangulateERKSt6vectorIS0_IN6linalg3vecIdLi2EEESaIS3_EESaIS5_EEd
```

In 3.1.0, ABI broke:
```
--- ...
+++ include/manifold/polygon.h       2025-05-14 20:50:31.000000000 +0100
@@ -52,10 +52,10 @@ using PolygonsIdx = std::vector<SimplePo
  * @brief Polygon triangulation
  *  @{
  */
-std::vector<ivec3> TriangulateIdx(const PolygonsIdx &polys, double epsilon = -1,
+std::vector<ivec3> TriangulateIdx(const PolygonsIdx& polys, double epsilon = -1,
                                   bool allowConvex = true);

-std::vector<ivec3> Triangulate(const Polygons &polygons, double epsilon = -1,
+std::vector<ivec3> Triangulate(const Polygons& polygons, double epsilon = -1,
                                bool allowConvex = true);
 /** @} */
 }  // namespace manifold
```

Signed-off-by: Sam James <sam@gentoo.org>

sci-mathematics/manifold/manifold-3.1.0-r1.ebuild

@@ -25,7 +25,7 @@ else
 fi
 
 LICENSE="Apache-2.0"
-SLOT="0"
+SLOT="0/1"
 
 IUSE="debug python +tbb test"
 REQUIRED_USE="python? ( ${PYTHON_REQUIRED_USE} )"

sci-mathematics/manifold/manifold-9999.ebuild

@@ -25,7 +25,7 @@ else
 fi
 
 LICENSE="Apache-2.0"
-SLOT="0"
+SLOT="0/1"
 
 IUSE="debug python +tbb test"
 REQUIRED_USE="python? ( ${PYTHON_REQUIRED_USE} )"