feat(ecs): add relation creation and removal detection to observers

[kuukitenshi]

Description

Added relation creation and removal detection to observers to allow .onRelate<ChildOf> and .onUnrelate<ChildOf>.

Checklist

• Self-review changes.
• Ensure test coverage.
• Add entry to the changelog's unreleased section.

[github-actions]

PR Preview Action v1.6.1
🚀 View preview at https://GameDevTecnico.github.io/cubos/preview/pr-1494/
Built to branch gh-pages at 2025-04-20 19:44 UTC. Preview will be ready when the GitHub Pages deployment is complete.

[codecov]

Codecov Report

Attention: Patch coverage is 60.82474% with 38 lines in your changes missing coverage. Please review.

Project coverage is 52.72%. Comparing base (78cda3b) to head (93da688).

Files with missing lines	Patch %	Lines
core/src/ecs/cubos.cpp	0.00%	34 Missing ⚠️
core/src/ecs/world.cpp	60.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1494      +/-   ##
==========================================
- Coverage   52.73%   52.72%   -0.02%     
==========================================
  Files         479      479              
  Lines       26261    26358      +97     
  Branches     2440     2455      +15     
==========================================
+ Hits        13848    13896      +48     
- Misses      12413    12462      +49     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[RiscadoA]

These observers must not rely on column ids, similarly to what we discussed regarding the entity destruction PR. This is because relations are stored in a different manner from components. We can discuss this later, ping me on discord when you pick this up