feat: show rule prevalence in result document

[Alessio-Falcini]

Description

This PR adds the rule prevalence information to the result document. This enhancement allows users to see how common a matched rule is, providing better context for analysis.

Changes

• Modified capa/render/result_document.py to include prevalence data in the output.
• Updated relevant tests in tests/test_result_document.py to verify the new field.

Motivation

Rule prevalence is a key indicator for analysts to distinguish between common behaviors and rare/anomalous capabilities. Including this in the standard result document makes the data more accessible

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[github-actions]

Please add bug fixes, new features, breaking changes and anything else you think is worthwhile mentioning to the master (unreleased) section of CHANGELOG.md. If no CHANGELOG update is needed add the following to the PR description: [x] No CHANGELOG update needed

[gemini-code-assist]

Summary of Changes

Hello @Alessio-Falcini, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the result document by incorporating rule prevalence information directly into the RuleMatches object. A new match_count field has been added to provide an explicit count of how many times a specific rule matched within an analyzed sample. This change aims to improve the accessibility of prevalence data in structured outputs, offering analysts a clearer context for distinguishing common behaviors from rare or anomalous capabilities without requiring additional processing.

Highlights

• New match_count field: Introduced a new match_count field to the RuleMatches class in capa/render/result_document.py. This field explicitly stores the number of matches for a rule, providing a convenience for structured outputs like JSON.
• Prevalence calculation: The from_capa method in capa/render/result_document.py now calculates and populates the match_count by counting the serialized_matches for each rule.
• Test coverage: Added a new test test_match_count_from_capa in tests/test_result_document.py to ensure the match_count field is correctly populated when a ResultDocument is regenerated from capa data.

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[gemini-code-assist]

Code Review

This pull request successfully introduces the rule prevalence information (match_count) into the result document, providing valuable context for analysis. The changes are well-implemented, including a clear definition of the new field in RuleMatches and its proper population during the from_capa conversion. The addition of serialized_matches improves readability and avoids redundant computation. Furthermore, the new test case test_match_count_from_capa thoroughly validates the functionality, ensuring the match_count field is correctly populated and accurate. Overall, this is a solid enhancement that improves the utility of the result document.

CHANGELOG updated or no update needed, thanks! 😄

[mr-tz]

Please see the issue discussion and open PR for the intent of this feature.