Move system stuff to the ecs/system directory

[RiscadoA]

Closes #643.

Description

Moves all system related code to the ecs/system dir.

Checklist

• Self-review changes.
• Evaluate impact on the documentation.

[github-actions]

PR Preview Action v1.4.4
🚀 Deployed preview to https://GameDevTecnico.github.io/cubos/pr-preview/pr-649/
on branch gh-pages at 2023-10-02 18:50 UTC

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (f65b241) 36.56% compared to head (263daf1) 36.56%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #649   +/-   ##
=======================================
  Coverage   36.56%   36.56%           
=======================================
  Files          92       92           
  Lines        6378     6378           
=======================================
  Hits         2332     2332           
  Misses       4046     4046           

Files	Coverage Δ
core/include/cubos/core/ecs/blueprint.hpp	94.73% <ø> (ø)
core/include/cubos/core/ecs/system/accessors.hpp	100.00% <ø> (ø)
core/include/cubos/core/ecs/system/commands.hpp	95.65% <ø> (ø)
core/include/cubos/core/ecs/system/dispatcher.hpp	82.14% <ø> (ø)
core/include/cubos/core/ecs/system/query.hpp	100.00% <ø> (ø)
core/include/cubos/core/ecs/system/system.hpp	79.12% <ø> (ø)
core/src/cubos/core/ecs/system/commands.cpp	97.29% <ø> (ø)
core/src/cubos/core/ecs/system/dispatcher.cpp	93.98% <ø> (ø)
core/src/cubos/core/ecs/system/system.cpp	100.00% <ø> (ø)

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