Delay wallet client construction until after logging, thread and other
init for two reasons:
- More responsive multiprocess GUI startup. When bitcoin-gui is started
this moves the call from bitcoin-gui to bitcoin-node that spawns
bitcoin-wallet off of the GUI event thread and onto the background GUI
init executor thread.
- Avoids feature_logging.py test failures with bitcoin-node by making
bitcoin-wallet logging start after bitcoin-node logging starts,
because the tests are not written to handle the bitcoin-wallet logging
init code running first.
This partially reverts commit b266b3e0bf,
moving wallet client creation back to the place it was located before.
optional_last_value, which does not throw, has replaced optional_value as
boost's default combiner. Besides being better supported, it also doesn't
trigger gcc's -Wmaybe-unitialized warning, presumably because exceptions no
longer bubble-up out of signals:
```bash
boost/signals2/last_value.hpp:54:36: warning: '*((void*)& value +1)' may be used uninitialized in this function [-Wmaybe-uninitialized]
if(value) return value.get();
```
The change in default happened in Boost 1.39.0 (along with the
introduction of the signals 2 library. More information is available here:
https://www.boost.org/doc/libs/1_73_0/doc/html/signals2/rationale.html#id-1.3.36.9.4
and here:
https://www.boost.org/doc/libs/1_73_0/doc/html/boost/signals2/optional_last_value.html
Co-authored-by: fanquake <fanquake@gmail.com>
