fix: Graphical issues with tint_config implementation

[usagirei]

Purpose of change (The Why)

Fix graphical issues introduced by #8026

Describe the solution (The How)

tint_config made use of std::optional<SDL_Color>, but std::nullopt and TILESET_NO_COLOR evaluated to different tiles (hash mismatch), when they should be the same, causing issues with dynamic tile lookup

Describe alternatives you've considered

N/A

Testing

Load Game
Change Tileset (e.g UltiCa) when the game is open
or Debug - Reload Tileset

Additional context

Note: Reloading/Changing the Tileset at z-level != 0 has its own issues, unrelated to this PR, and will be dealt with later.

Aditionally:

std::optional<float> contrast;    
std::optional<float> saturation;
std::optional<float> brightness;

Are prone to the same issue, and should also be changed to be always present values, with bias (-1 ~ 1 range), and 0 being treated as no-op like TILESET_NO_COLOR

Tagging @AzmodiusX for this

Checklist

Mandatory

• I wrote the PR title in conventional commit format.
• I ran the code formatter.
• I linked any relevant issues using github keyword syntax like closes #1234 in Summary of the PR so it can be closed automatically.
• I've committed my changes to new branch that isn't main so it won't cause conflict when updating main branch later.

[AzmodiusX]

I'm going to swap the post processing fields to be non-optional as well, but I need to handle other stuff.
Please don't merge this beforehand.

[AzmodiusX]

Everything seems to work perfectly.
My additions were minor, so I'll approve
But I'll let someone else merge, just in case