fix: 描画まわりのレビュー指摘（#7・#10・#11・#12）を修正 - #62

The face where the two halves touch was hidden whenever both halves had
the same DoubleSlabVariant, but NON_OPAQUE groups different materials
(leaves, glowstone, ...). A glowstone half under a leaf half lost its top
face, so the ground showed through the leaves (review #7).

Now the face is drawn exactly when the same two blocks stacked as full
blocks would draw it: hidden under an opaque block or between matching
glass, visible otherwise. A GameTest compares 100 material pairs against
full blocks placed in the world.

shouldDrawSide runs for every face of every block while building chunk
meshes. Check the block type before touching the world or block entities.

Scene capture: allow fixing the FPS cap with -Dslabee.scene.maxFps and
disable autosave while capturing.

Light propagation runs after blocks are placed. Shooting before it ends
made the ground shading around double slabs differ from run to run.

Disabling saving appears to make chunks that are unloaded while the camera
moves come back with recomputed light, so the ground shading differed
between runs. Under investigation; determinism check in progress.