[3.13] gh-121610: pyrepl - handle extending blocks when multi-statement blocks are pasted (GH-121757) (GH-121825)

console.compile with the "single" param throws an exception when
there are multiple statements, never allowing to adding newlines
to a pasted code block (gh-121610)

This adds a few extra checks to allow extending when in an indented
block, and tests for a few examples.

(cherry picked from commit 7d111dac160c658b277ec0fac75eee8edcfbe9dc)

Co-authored-by: saucoide <32314353+saucoide@users.noreply.github.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>