[VRAD] small improvements

[Unusuario2]

This PR increases the lighting quality of VRAD:
1: When working with low luxel scales or large surfaces in the Source engine, lighting from the environment light (with -softsun enabled) can appear dirty due to a low number of samples. This PR addresses the issue by improving sample density.

For Users:
Although the default value is 30, you can safely increase it up to 1024 or even 16384. Increasing this value has a negligible impact on computation time (a few seconds or minutes more). For optimal results:

Use -SunSamplesAreaLight 1024 for general improvements.
Use -SunSamplesAreaLight 4096 for very very large surfaces where extensive sunlight coverage occurs.

-SunSamplesAreaLight 30 (old vrad stock value)

-SunSamplesAreaLight 8192

2: In many cases where a big levels have a large portal leaf, ambient lighting become less accurate for bounced light. Allowing the user to increase the number of ambient cubes with the -AmbientCubesPerLeaf N command helps solve this issue, also makes lighting of static props more acurate.

For users: The -AmbientCubesPerLeaf N command sets the number of ambient light cubes used for lighting calculations. N represents the number of ambient cubes you want VRAD to generate. VRAD will optimize the number of ambient cubes based on their RGB values (if they are very similar and close to each other, some ambient cubes will be deleted).

-AmbientCubesPerLeaf 16 (vrad stock value)

-AmbientCubesPerLeaf 64

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• My PR follows all guidelines in the CONTRIBUTING.md file
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