Fix false positives in UploadSecurityExtractor

[google-labs-jules]

Fixes multiple false positives in the UploadSecurityExtractor. The regexes for KEY_FROM_NAME, TRUST_CLIENT_MIME, and ACCEPT_SVG were too broad, flagging benign usages like logging req.file.mimetype or rejecting image/svg+xml.

Changes:

• Bounded KEY_FROM_NAME to ensure it only matches when assigned directly to a key/path variable (e.g. Key: req.file.originalname).
• Updated TRUST_CLIENT_MIME to negative lookbehind common logger functions (console.log, logger.info, etc.).
• Addressed SVG flagging using stricter bounded matches that exclude cases when a rejection logic acts on the condition.
• Added regression test test_upload_security_benign_fps containing benign samples to ensure FPs do not regress.
• Verified test suite passes fully, zero true-positive regressions. CHANGELOG updated and docguard remains fully compliant.

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PR created automatically by Jules for task 15582470766821012324 started by @raccioly

[google-labs-jules]

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