fix: change environment saving in HDR Environment.

[Felix Frank (feliopterix)]

1. Why is this change necessary?

The current implementation leads to errors when instantiating dive (without auto-starting), then changing the scene background, then starting render process.

This happens in Shopware Scene Editor atm: We instantiate dive, load the scene resources, apply them in dive and then start rendering.

2. What does this change do, exactly?

Extend the background management in the HDR Environment so that it always restores the correct scene background.

3. Describe each step to reproduce the issue or behaviour.

4. Please link to the relevant issues (if any).

5. Checklist

• I have rebased my changes to remove merge conflicts
• I have written tests and verified that they fail without my change
• I have written or adjusted the documentation according to my changes
• This change has comments for package types, values, functions, and non-obvious lines of code
• I have read the contribution requirements and fulfil them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.70%. Comparing base (d33e39c) to head (d1790ec).
⚠️ Report is 11 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk     #221      +/-   ##
==========================================
+ Coverage   99.69%   99.70%   +0.01%     
==========================================
  Files         141      141              
  Lines        7435     7441       +6     
  Branches     1723     1737      +14     
==========================================
+ Hits         7412     7419       +7     
+ Misses         23       22       -1     

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