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/cave_path.cpp

@@ -6,10 +6,9 @@
 
 #include <algorithm>
 namespace Cubed {
-CavePath::CavePath(unsigned int world_seed, int path_id,
+CavePath::CavePath(unsigned int chunk_seed, unsigned world_seed,
                    const glm::vec3& start_pos) {
-    m_path_id = path_id;
-    m_seed = HASH::combine_32(world_seed, path_id);
+    m_seed = HASH::combine_32(chunk_seed, world_seed);
     m_random.init(m_seed);
     m_yaw = m_random.random_float(0.0f, 360.0f);
     m_pitch = m_random.random_float(-10.0f, 10.0f);
@@ -75,7 +74,8 @@ void CavePath::precompute_chunk_coverage() {
 
         for (int cx = min_cx; cx <= max_cx; ++cx)
             for (int cz = min_cz; cz <= max_cz; ++cz)
-                m_pending_chunks.insert({cx, cz});
+                m_pending_chunks.insert(
+                    std::make_pair(ChunkPos{cx, cz}, false));
     }
 }