Improve curses documentation

[serhiy-storchaka]

There are some typos, factual errors and missing details in curses documentation.

Linked PRs

• gh-151623: Improve curses documentation and docstrings #151625
• [3.15] gh-151623: Improve curses documentation and docstrings (GH-151625) #151628
• [3.14] gh-151623: Improve curses documentation and docstrings (GH-151625) #151629
• [3.13] gh-151623: Improve curses documentation and docstrings (GH-151625) (GH-151629) #151630
• gh-151623: Add missing curses docstrings and document intrflush() #151632
• gh-151623: Improve curses documentation style #151635
• [3.15] gh-151623: Improve curses documentation style (GH-151635) #151636
• [3.14] gh-151623: Improve curses documentation style (GH-151635) #151637
• [3.13] gh-151623: Improve curses documentation style (GH-151635) #151638
• [3.15] gh-151623: Add missing curses docstrings and document intrflush() (GH-151632) #151641
• [3.14] gh-151623: Add missing curses docstrings and document intrflush() (GH-151632) #151642