[fix] ecdsa sig_is_valid bug

[zhenfeizhang]

Description

Previously, sig_is_valid in the ecdsa-circuit is checked and enforced within circuit. That means we cannot prove a signature is invalid. This PR makes sig_is_valid a return value so the caller can assert a tx is invalid.

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

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

Design choices

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[lispc]

we can merge this after ci passes

[zhenfeizhang]

we can merge this after ci passes

Fixed