feat(reporting): fix #504 by implementing Soroban Audit Evidence Generator

[TochukwuJustice]

closes #504
This PR addresses issue #504 to provide traceable supporting evidence for findings generated by the GasGuard analyzer. Previously, findings were simply reported but lacked the verifiable file evidence and detailed documentation references required for robust audits.

The new flow utilizes the stellarKB to link finding rules with their full explanations and documentation links. Additionally, it reads the original source code directly using a caching mechanism to extract snippets safely padded with contextual lines. This change matters significantly as it creates a direct, provable link between the tool's finding and the underlying code, enabling accurate human review and CI tracking.

Implementation details:

• Created the SorobanEvidenceGenerator class to process findings into Evidence artifacts.
• Implemented extractCodeSnippet which manages a file I/O cache to prevent redundant disk reads for the same source file.
• Enabled JSON artifact exports.

4. Changes Made

• src/reporting/evidence/stellar/types.ts: Added interface definitions for Evidence, CodeSnippet, and configuration options. (Addresses Implement Soroban Audit Evidence Generator #504)
• src/reporting/evidence/stellar/evidence-generator.ts: Implemented core logic including memoized snippet extraction and kb enrichment. (Addresses Implement Soroban Audit Evidence Generator #504)
• src/reporting/evidence/stellar/index.ts: Exported the generator and types. (Addresses Implement Soroban Audit Evidence Generator #504)
• src/reporting/evidence/stellar/evidence-generator.spec.ts: Unit test suite to verify code extraction and file generation correctness. (Addresses Implement Soroban Audit Evidence Generator #504)
• src/tsconfig.json: Created to ensure the IDE type-checks test files safely within src/.

5. Testing

The following commands were executed to verify the functionality:

npx jest src/reporting/evidence/stellar/evidence-generator.spec.ts