A new config API is introduced, and ~all of the codebase is adapted to it.
The old API is kept but mainly only for dynamic usage where its extra flexibility is needed.
Using examples, the old config API looked this:
```
>>> config.get("request_expiry", 86400)
604800
>>> config.set_key("request_expiry", 86400)
>>>
```
The new config API instead:
```
>>> config.WALLET_PAYREQ_EXPIRY_SECONDS
604800
>>> config.WALLET_PAYREQ_EXPIRY_SECONDS = 86400
>>>
```
The old API operated on arbitrary string keys, the new one uses
a static ~enum-like list of variables.
With the new API:
- there is a single centralised list of config variables, as opposed to
these being scattered all over
- no more duplication of default values (in the getters)
- there is now some (minimal for now) type-validation/conversion for
the config values
closes https://github.com/spesmilo/electrum/pull/5640
closes https://github.com/spesmilo/electrum/pull/5649
Note: there is yet a third API added here, for certain niche/abstract use-cases,
where we need a reference to the config variable itself.
It should only be used when needed:
```
>>> var = config.cv.WALLET_PAYREQ_EXPIRY_SECONDS
>>> var
<ConfigVarWithConfig key='request_expiry'>
>>> var.get()
604800
>>> var.set(3600)
>>> var.get_default_value()
86400
>>> var.is_set()
True
>>> var.is_modifiable()
True
```
If the user had `config.get("show_crash_reporter")==False`, they would
never get to see excs collected via `send_exception_to_crash_reporter(exc)`.
E.g.:
```
E | gui.qt.ElectrumGui | error loading wallet (or creating window for it)
Traceback (most recent call last):
File "/opt/electrum/electrum/gui/qt/__init__.py", line 433, in main
if not self.start_new_window(path, self.config.get('url'), app_is_starting=True):
File "/opt/electrum/electrum/gui/qt/__init__.py", line 307, in wrapper
return func(self, *args, **kwargs)
File "/opt/electrum/electrum/gui/qt/__init__.py", line 332, in start_new_window
wallet = self._start_wizard_to_select_or_create_wallet(path)
File "/opt/electrum/electrum/gui/qt/__init__.py", line 377, in _start_wizard_to_select_or_create_wallet
db = WalletDB(storage.read(), manual_upgrades=False)
File "/opt/electrum/electrum/wallet_db.py", line 73, in __init__
self.load_data(raw)
File "/opt/electrum/electrum/wallet_db.py", line 104, in load_data
self._after_upgrade_tasks()
File "/opt/electrum/electrum/wallet_db.py", line 202, in _after_upgrade_tasks
self._load_transactions()
File "/opt/electrum/electrum/util.py", line 439, in <lambda>
return lambda *args, **kw_args: do_profile(args, kw_args)
File "/opt/electrum/electrum/util.py", line 435, in do_profile
o = func(*args, **kw_args)
File "/opt/electrum/electrum/wallet_db.py", line 1310, in _load_transactions
self.data = StoredDict(self.data, self, [])
File "/opt/electrum/electrum/json_db.py", line 79, in __init__
self.__setitem__(k, v)
File "/opt/electrum/electrum/json_db.py", line 44, in wrapper
return func(self, *args, **kwargs)
File "/opt/electrum/electrum/json_db.py", line 97, in __setitem__
v = self.db._convert_dict(self.path, key, v)
File "/opt/electrum/electrum/wallet_db.py", line 1361, in _convert_dict
v = dict((k, SwapData(**x)) for k, x in v.items())
```
Previously if there was a chain of exceptions, we were only
sending the traceback for the final exception.
E.g.
try:
raise ExcOne("asdasd")
except ExcOne() as e:
raise ExcTwo("qweqwe") from e
^ we would lose all info about ExcOne, including potentially many lines of trace
related #4905
related Electron-Cash/Electron-Cash@6a3d76b0ab
conceptually did not really make sense that the Exception_Hook kept a reference
to an ~arbitrary main window (preventing gc)
