rust-discovery: moving most of hg-cpython methods to regular code blocks
The chosen methods are those with conversion of an incoming Python iterable,
as they will be changed the most when we will remove the C index, and
`takefullsample` for consistency with `takequicksample`.
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL