testool: support sub circuit; fix modexp row usage

[lispc]

Description

[PR description]

Issue Link

[link issue here]

Type of change

• 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

Contents

• [item]

Rationale

[design decisions and extended information]

How Has This Been Tested?

[explanation]

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MUST: Reference the issue to resolve

Single responsability

Is RECOMMENDED to create single responsibility commits, but not mandatory.

Anyway, you MUST enumerate the changes in a unitary way, e.g.

This PR contains:
- Cleanup of xxxx, yyyy
- Changed xxxx to yyyy in order to bla bla
- Added xxxx function to ...
- Refactored ....

Design choices

RECOMMENDED to:

• What types of design choices did you face?
• What decisions you have made?
• Any valuable information that could help reviewers to think critically