feat(client-player): add block cooldown and track mouse state

Introduce a time-based cooldown for block placement (PLACE_BLOCK_INTERVAL) to prevent rapid clicking. Replace the global InputState with per-player MouseState tracking in ClientPlayer. Rename place_block() to get_current_block() for clarity. Remove the old src/input.cpp and the Cubed/input.hpp header, moving input structures to Cubed/input/input.hpp.

src/CMakeLists.txt

@@ -9,7 +9,6 @@ target_sources(${PROJECT_NAME}
         gameplay/biome.cpp
         gameplay/chunk_generator.cpp
         gameplay/tree.cpp
-        input.cpp
         render/renderer.cpp
         shader.cpp
         texture_manager.cpp