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

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

Co-authored-by: Łukasz Langa <lukasz@langa.pl>