fix(block and several others): deprecate title struct, it's position, and related functions

[TadoTheMiner]

I've deprecated Title, the title() function, Position, and the titles_position() function, and adapted the docs to have title_top() and title_bottom() in examples. While it was suggested to add top_title() and bottom_title(), and deprecate the old ones, there's no need because title_top() and title_bottom() have the same signatures, as the new functions would. It was also suggested that we add the top_titles and bottom_titles fields, this is currently not possible since the title() function supports having titles with no position. So we should rather add the fields after removing the deprecations. I was forced to add #![cfg_attr(test, allow(deprecated)] to lib.rs due to a rust bug. And you can ignore flake.nix and flake.lock, it's for Nix users, as I've switched to NixOS recently.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.2%. Comparing base (9bd89c2) to head (942ea3f).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1061     +/-   ##
=======================================
- Coverage   94.3%   94.2%   -0.1%     
=======================================
  Files         61      61             
  Lines      14768   14770      +2     
=======================================
- Hits       13932   13922     -10     
- Misses       836     848     +12     

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[TadoTheMiner]

I've added TitlePosition enum and title_at_position function in block.rs (which calls title_top and title_bottom). The reason why I did so, is because a person using this function

fn foo(position: Position) -> Block {
    Block::new().title(Title::from("bar").position(position))
}

would have to write their own enum since Position is deprecated.
Position is now pub use ratatui::widgets::block::TitlePosition and no longer an enum.

[TadoTheMiner]

Forgot mention issue #738