Most users don't read the content of the wallet files, and for debugging it is easy to convert the format to pretty JSON:
`cat wallet_file | python -c'import fileinput, json; print(json.dumps(json.loads("".join(fileinput.input())), sort_keys=True, indent=4))'`
The gain is a 20% reduction in file size for unencrypted wallets, and a 100+% speed improvement when writing the wallet to disk.
Before:
```
pierre@simak:~/.electrum-abc$ ls -lrth ../.electrum-abc_bck_2023-07-07/wallets/
-rw------- 1 pierre pierre 15K juil. 7 09:30 default_wallet
-rw-r--r-- 1 pierre pierre 2,0M juil. 7 09:30 test_wallet
-rw-r--r-- 1 pierre pierre 986K juil. 7 09:30 default_encr
-rw------- 1 pierre pierre 110M juil. 7 09:30 ifp_addr
pierre@simak:~/dev/bitcoin-abc/electrum$ ./electrum-abc -v
| 14.088| |04| [profiler] WalletStorage.write 0.9765
| 15.629| |04| [profiler] WalletStorage.write 0.9118
| 34.379| |00| [profiler] WalletStorage.write 0.9347
```
After:
```
$ ./electrum-abc -v
| 14.503| |04| [profiler] WalletStorage.write 0.4619
| 15.696| |04| [profiler] WalletStorage.write 0.3535
| 35.000| |00| [profiler] WalletStorage.write 0.3855
| 35.838| |00| [profiler] WalletStorage.write 0.3627
pierre@simak:~/.electrum-abc$ ls -lrth wallets
-rw-r--r-- 1 pierre pierre 959K juil. 9 09:53 default_encr
-rw-r--r-- 1 pierre pierre 1,6M juil. 9 09:54 test_wallet
-rw------- 1 pierre pierre 14K juil. 9 09:54 default_wallet
-rw------- 1 pierre pierre 90M juil. 9 09:55 ifp_addr
```
Encrypted wallet files already used compact JSON, so this is a very minor improvement by removing spaces from delimiters.