feat(examples): add multi-backend support

[junkdog]

This merge request implements the multi-backend functionality discussed in #103. It adds the ability to switch between different rendering backends (DOM, Canvas, WebGL2) on the fly (reloads the application), along with a real-time FPS counter.

Changes

New Shared Library (examples/shared/)

• Backend switching: Query parameter support (?backend=webgl2)
• FPS tracking: Real-time performance monitoring
• Visual footer: Backend switcher with current backend and FPS display
• Unified API: backend_from_query_param() for consistent backend creation

Updated Examples

Modified all 17 examples to use the new multi-backend system:

// Before
let backend = DomBackend::new()?;
let terminal = Terminal::new(backend)?;

// After  
let (_backend_type, terminal) = backend_from_query_param(BackendType::Dom)
    .webgl2_options(WebGl2BackendOptions::new().measure_performance(true)) // per-backend options
    .build_terminal()?;

Features

• Real-time FPS: Automatic tracking and display
• Visual switcher: Fixed footer with clickable backend links

[junkdog]

if #108 is merged before this one, some examples should be updated with the new options for hyperlinks

[orhun]

This is so neat! Thanks <3

It requires a refactor and we should be set

[junkdog]

there, i think everything above has been addressed

[orhun]

Neat, LGTM!