refactor: world generation (#17)

* refactor: use TBB for concurrent hash maps and parallelize chunk processing

* fix: tbb link fail

* refactor(chunk): remove biome check for caves in rivers and oceans

* refactor(random): replace std distributions with custom implementations

Avoid overhead and platform-dependent behavior of `<random>` distributions by using direct engine operations and integer arithmetic. This ensures deterministic, cross-platform results and improves performance.

* refactor(generation): use chunk seed for cave and river paths

- Use per-chunk seed instead of global path_id for cave and river generation.
- Remove unused m_sum variables and m_path_id members.
- Clamp river yaw within 10 degrees of initial direction.
- Fix river radius interpolation (use t instead of 1-t).
- Lower sea level from 64 to 63.

src/gameplay/chunk.cpp

@@ -103,8 +103,7 @@ int Chunk::index(const glm::vec3& pos) {
     return Chunk::index(pos.x, pos.y, pos.z);
 }
 
-void Chunk::gen_vertex_data(
-    const std::array<const std::vector<BlockType>*, 4>& neighbor_block) {
+void Chunk::gen_vertex_data(const OptionalBlockVectorArray& neighbor_block) {
     if (m_is_on_gen_vertex_data) {
         return;
     }
@@ -265,8 +264,7 @@ unsigned Chunk::seed() const {
 
 BiomeConditions& Chunk::conditions() { return m_conditions; }
 
-void Chunk::gen_vertices(
-    const std::array<const std::vector<BlockType>*, 4>& neighbor_block) {
+void Chunk::gen_vertices(const OptionalBlockVectorArray& neighbor_block) {
     static const glm::ivec3 DIR[6] = {{0, 0, 1},  {1, 0, 0}, {0, 0, -1},
                                       {-1, 0, 0}, {0, 1, 0}, {0, -1, 0}};
 
@@ -299,8 +297,9 @@ void Chunk::gen_vertices(
                             World::chunk_pos(world_nx, world_nz);
 
                         auto is_culled =
-                            [&](const std::vector<BlockType>* chunk_blocks) {
-                                if (chunk_blocks == nullptr) {
+                            [&](const std::optional<std::vector<BlockType>>&
+                                    chunk_blocks) {
+                                if (chunk_blocks == std::nullopt) {
                                     return true;
                                 }
                                 int x, y, z;