New tokens arquitecture POC

[GomezIvann]

Checklist

• [x] The build process is done without errors. All tests pass in the /lib directory.
• [x] Self-reviewed the code before submitting.
• [x] Meets accessibility standards.
• [x] Added/updated documentation to /website as needed.
• [x] Added/updated tests as needed.

Purpose A test for the new tokens architecture.

Description This PR includes:

• New CSS files for global styling: fonts.css and tokens.css.
• inyectStyles flag for default styling within the library build.
• New exported function setCustomTheme (provisional name) for application-level theming (only once intented per application).
• New exported provider HalstackThemeProvider (provisional name) for dynamic and specific theming strategies.
• Button code page example.