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
```
- wallet.add_input_info() previously had a fallback to download parent
prev txs from the network (after a lookup in wallet.db failed).
wallet.add_input_info() is not async, so the network request cannot
be done cleanly there and was really just a hack.
- tx.add_info_from_wallet() calls wallet.add_input_info() on each txin,
in which case these network requests were done sequentially, not concurrently
- the network part of wallet.add_input_info() is now split out into new method:
txin.add_info_from_network()
- in addition to tx.add_info_from_wallet(), there is now also tx.add_info_from_network()
- callers of old tx.add_info_from_wallet() should now called either
- tx.add_info_from_wallet(), then tx.add_info_from_network(), preferably in that order
- tx.add_info_from_wallet() alone is sufficient if the tx is complete,
or typically when not in a signing context
- callers of wallet.bump_fee and wallet.dscancel are now expected to have already
called tx.add_info_from_network(), as it cannot be done in a non-async context
(but for the common case of all-inputs-are-ismine, bump_fee/dscancel should work regardless)
- PartialTxInput.utxo was moved to the baseclass, TxInput.utxo
(this somehow escaped attention before, as most objects usually don't have multiple instances,
unless multiple wallets are open at the same time.)
Also, move all signal declarations, class constants and variables to the top of class definitions.
