feat(prelude): add a prelude

[joshka]

This allows users of the library to easily use ratatui without a huge amount of imports

Review hints:

• The main change is lib.rs
• I'm curious whether the aliasing decisions make sense (BlockTitle, CanvasLine, etc.)
• Are there any types included in the prelude that are too generic and clash with commonly used rust types?

[codecov]

Codecov Report

Merging #304 (2e29558) into main (a1813af) will not change coverage.
The diff coverage is n/a.

❗ Current head 2e29558 differs from pull request most recent head c49c665. Consider uploading reports for the commit c49c665 to get more accurate results

@@           Coverage Diff           @@
##             main     #304   +/-   ##
=======================================
  Coverage   83.11%   83.11%           
=======================================
  Files          37       37           
  Lines        7717     7717           
=======================================
  Hits         6414     6414           
  Misses       1303     1303           

Impacted Files	Coverage Δ
src/lib.rs	100.00% <ø> (ø)
src/widgets/block.rs	86.10% <ø> (ø)

[joshka]

(added StatefulWidget)

[orhun]

Good idea.