Fix unconfirmed balances in getBalance

[phoenix-web3]

Description

Electrum has been updated with this piece of code:

async def get_balance_for_scripthash(self, sh: str) -> dict:
        if not is_hash256_str(sh):
            raise Exception(f"{repr(sh)} is not a scripthash")
        # do request
        res = await self.session.send_request('blockchain.scripthash.get_balance', [sh])
        # check response
        assert_dict_contains_field(res, field_name='confirmed')
        assert_dict_contains_field(res, field_name='unconfirmed')
        assert_non_negative_integer(res['confirmed'])
        assert_integer(res['unconfirmed'])
        return res

This change fix the bug that causes getBalance to fail for transactions with negative unconfirmed balance

Thanks to @coval3nte

Fixes #76 (issue)

Issue #110 will be marked as wontfix

Dependencies (if any)

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Related PR or Docs PR

• Issue cculianu/Fulcrum#105
• get_balance_for_scripthash
• Issue spesmilo/electrum#7684
• PR spesmilo/electrum#7685

Good practices to consider

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules