Replace stl execution policies with pstl equivalents in Swarm

Flock/flock/src/swarm/Swarm.cc

 #include "Swarm.hh"
 
+#include <pstl/algorithm>
+#include <pstl/execution>
+
 #include "../util/Misc.hh"
 
 glm::ivec3 flock::Swarm::getVoxelIndex(const glm::vec3& pos) const
@@ -159,7 +162,7 @@ void flock::Swarm::tick(float dt)
         mVoxelCache.clear();
 
         auto view = mRegistry->view<TransformC, SwarmlingC>();
-        std::for_each(std::execution::seq, view.begin(), view.end(), [&](auto const ent) {
+        std::for_each(pstl::execution::seq, view.begin(), view.end(), [&](auto const ent) {
             auto& swarmling = mRegistry->get<SwarmlingC>(ent);
             mVoxelCache[getVoxelIndex(swarmling.position)].emplace_back(
                 VoxelCacheSwarmling{ent, swarmling.position, swarmling.velocity});
@@ -172,7 +175,7 @@ void flock::Swarm::tick(float dt)
         // NOTE: std::execution::parallel_unsequenced_policy
         // Only call thread safe methods here
         auto view = mRegistry->view<TransformC, SwarmlingC>();
-        std::for_each(std::execution::par_unseq, view.begin(), view.end(),
+        std::for_each(pstl::execution::par_unseq, view.begin(), view.end(),
                       [&](auto const ent) { updateSwarmling(ent, mRegistry->get<SwarmlingC>(ent)); });
     }
 
@@ -182,7 +185,7 @@ void flock::Swarm::tick(float dt)
         // NOTE: std::execution::parallel_unsequenced_policy
         // Only call thread safe methods here
         auto view = mRegistry->view<TransformC, SwarmlingC>();
-        std::for_each(std::execution::par_unseq, view.begin(), view.end(), [&](auto const ent) {
+        std::for_each(pstl::execution::par_unseq, view.begin(), view.end(), [&](auto const ent) {
             auto& swarmling = mRegistry->get<SwarmlingC>(ent);
             auto& transform = mRegistry->get<TransformC>(ent);
             swarmling.velocity = clampVectorLength(swarmling.velocity + swarmling.acceleration * dt, mMaxVelocity);

Flock/flock/src/swarm/Swarm.hh

 #pragma once
 
 #include <atomic>
-#include <execution>
 #include <iostream>
 #include <random>
 #include <unordered_map>