"Run the numbers" shall use muhash

**Describe the bug**
Or it should be at least possible to set `muhash` when calling `gettxoutsetinfo`. Using the `coinstatsindex` make it take a second instead of minutes.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to `http://127.0.0.1:25441/wallets/wallet//receive/`
2. Click on 'Run the numbers!'
3. It takes too long since running `gettxoutsetinfo` without `muhash` parameter is very slow. With `muhash` parameter, one has to have the small (currently 131MB) `coinstatsindex`.

**Expected behavior**
"Run the numbers" should take less than a second. It should be immediate.

```
$ time bitcoin-cli gettxoutsetinfo muhash
{
"height": 775192,
"bestblock": "000000000000000000071fafcd59fb89454864d51afc206559111381b22cb630",
"txouts": 83747992,
"bogosize": 6243049379,
"muhash": "fae547fb57efe29fcb36c9caf39114543c5d827d8b0831147ad0f0136dc90a22",
"total_amount": 19282240.19258451,
"total_unspendable_amount": 216.05741549,
"block_info": {
"prevout_spent": 6465.64625252,
"coinbase": 6.41212171,
"new_outputs_ex_coinbase": 6465.48413081,
"unspendable": 0.00000000,
"unspendables": {
"genesis_block": 0.00000000,
"bip30": 0.00000000,
"scripts": 0.00000000,
"unclaimed_rewards": 0.00000000
}
}
}
0m00.02s real 0m00.00s user 0m00.00s system
```

**Desktop (please complete the following information):**
- Where is your node running: local full node (plain Bitcoin Core on Linux, no bundles)
- Where is your specter running: pip3 local Linux x86_64
- Browser Chrome
- Specter Version 1.14.5

Start at the wallet receive page at /wallets/wallet//receive/ and trace the "Run the numbers!" action to the gettxoutsetinfo call. Check how the muhash parameter and coinstatsindex are handled, then verify that the action completes promptly and returns the expected result.

Written by the indexing model from the issue text.