fix(scope): expectation signatures structured output is not keyed like configured in contract output element

[antoinemzs]

Description

structured output sent as

{ "signatures" : { "targets".... } }

Contract output element is configured as

expectation_signature = ContractOutputElement(
    type=ContractOutputType.ExpectationSignature,
    field="expectation_signature",
    isMultiple=True,
    isFindingCompatible=False,
    labels=["scan"],
)

Environment

1. OS: { e.g. macOS 14, Windows 11, Ubuntu 22.04, etc. }
2. Version: { e.g. 1.2.3 }
3. Other environment details:

Reproducible steps

Steps to create the smallest reproducible scenario:

1. { e.g. Run ... }
2. { e.g. Click ... }
3. { e.g. Error ... }

Expected output

Actual output

Additional information