gh-135621: Simplify TermInfo

[encukou]

_pyrepl.terminfo's terminfo parsing follows ncurses and does a bunch of unnecessary (and untested) work. It can be simplified:

• Don't parse names, booleans, and numbers. (I hope I left enough code & comments to make it easy to add these if needed.)
• Don't store the strings as a list; populate the dict directly.
• Use struct.iter_unpack and string_table.find instead of for loops

• Issue: Misleading pyrepl warnings when _curses module is missing #135621

[miss-islington-app]

Thanks @encukou for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-136925 is a backport of this pull request to the 3.14 branch.