Bound SemVer input length - #24100

Vulns::Semver parses version strings from remote advisory data without a size limit. Large strings reach regex matching, integer conversion and prerelease splitting.

Reject inputs over 256 bytes before normalisation or parsing. Oversized versions return nil, as invalid versions already do, so the advisory matcher retains the OSV match without reporting a local fix. Cover the limit boundary, oversized numeric components, build metadata and whitespace, plus advisory matching.

From the repository root, run:

./bin/brew ruby -- -e 'require "vulns/semver"; p Homebrew::Vulns::Semver.compare("1.0.0-" + "a" * 5000, "1.0.0")'

This prints -1 before the change and nil after it. The limit also applies to release_version.

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

OpenAI Codex (GPT-6) assisted with the implementation and tests.