feat: Color themes

[bladecoder]

Hello!

This pull request introduces a new color theme system to the Mousefood embedded terminal library, allowing users to customize how Ratatui colors are mapped to display pixels. The changes include a new ColorTheme struct with built-in themes, updates to the backend to support color themes, and refactoring of color conversion logic.

Colors can be remapped using color_theme on EmbeddedBackendConfig.
By default the ANSI palette is used.

use mousefood::{ColorTheme, EmbeddedBackend, EmbeddedBackendConfig};
use mousefood::embedded_graphics::pixelcolor::Rgb888;

let theme = ColorTheme {
    background: Rgb888::new(5, 5, 5),
    foreground: Rgb888::new(240, 240, 240),
    yellow: Rgb888::new(255, 200, 0),
    ..ColorTheme::ansi()
};

let config = EmbeddedBackendConfig {
    color_theme: theme,
    ..Default::default()
};
let backend = EmbeddedBackend::new(&mut display, config);

Besides, the Tokio Night color theme has been included as a built-in theme.

use mousefood::{ColorTheme, EmbeddedBackendConfig};

let config = EmbeddedBackendConfig {
    color_theme: ColorTheme::tokionight(),
    ..Default::default()
};

Below an example of the ansi and Tokio Night themes working with the emulator example:

[orhun]

This looks pretty good!

[bladecoder]

Hey @orhun, thanks for the review! By the way, I loved your talk about embedded ratatouille at the Tokyo Rust meetup!

[orhun]

LGTM, thanks!

[orhun]

Oops, there seems to be some clippy issues, can you address them? (If not I can get to this soon)

error: this function has too many arguments (8/7)
   --> mousefood/src/backend.rs:126:5
    |
126 | /     fn init(
127 | |         display: &'display mut D,
128 | |         flush_callback: impl FnMut(&mut D) + 'static,
129 | |         font_regular: MonoFont<'static>,
...   |
134 | |         color_theme: ColorTheme,
135 | |     ) -> EmbeddedBackend<'display, D, C> {
    | |________________________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.93.0/index.html#too_many_arguments
    = note: `-D clippy::too-many-arguments` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::too_many_arguments)]`

error: methods with the following characteristics: (`to_*` and `self` type is `Copy`) usually take `self` by value
   --> mousefood/src/colors.rs:147:18
    |
147 |     fn to_rgb888(&self) -> Rgb888 {
    |                  ^^^^^
    |
    = help: consider choosing a less ambiguous name
    = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.93.0/index.html#wrong_self_convention
    = note: `-D clippy::wrong-self-convention` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::wrong_self_convention)]`

error: could not compile `mousefood` (lib) due to 2 previous errors

We could create a separate struct for mitigating too_many_arguments I believe.

[bladecoder]

Fixed the clippy problems. Sorry for not checking before 😓

[orhun]

thanks again!