twacube_to_twa: allows use of existing BDD_dict

* spot/twacube_algos/convert.cc,
spot/twacube_algos/convert.hh: Here.
* tests/core/twacube.cc: Test it.
9 jobs for er/tmp in 171 minutes and 56 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #93479
alpine-gcc

00:51:30

passed #93480
arch-clang

00:52:12

passed #93481
arch-gcc-glibcxxdebug

01:17:00

passed #93478
debian-gcc-snapshot

01:31:30

passed #93476
debian-stable-gcc

01:17:10

passed #93477
debian-unstable-gcc-coverage

01:14:59

89.6%
passed #93482
mingw-shared

00:09:00

passed #93483
mingw-static

00:10:37

passed #93484
armv7
raspbian

01:36:18