[TEST] Adding Test Cases for Circom Proving

[AtelyPham]

Is your feature request related to a problem? Please describe.
Currently, there are no test cases available for Circom proving classes, making it challenging to ensure that any updates to the code of these classes still perform as intended.

Describe the solution you'd like

To address this, I suggest writing test cases similar to the ones available for Arkwork proving. These test cases are already available in the webb.js repository.

Additional context

• The Circom proving classes can be found at https://github.com/webb-tools/webb.js/tree/master/packages/sdk-core/src/proving/circom.
• Test cases are already available for Arkwork proving at https://github.com/webb-tools/webb.js/blob/master/packages/sdk-core/src/__test__/arkworks-proving.spec.ts.