test: add cross-layer, false positive, and mixed obfuscation adversarial payloads

[Ananya44444]

Extends the adversarial payload library from #5 with additional real-world attack patterns.

Additions
Cross-layer payloads where malicious intent emerges post-normalization/decoding
False positive test case to evaluate precision and avoid overblocking
Mixed obfuscation payload combining zero-width characters and homoglyphs

Motivation
The current taxonomy focuses on layer-isolated behavior. These additions help validate:
Correct stage ordering (Normalize → Scan)
Robustness against encoding-based evasion chains
Precision of detection systems (false positives)

Built on top of #5

[Copilot]

Pull request overview

Extends the adversarial payload taxonomy under tests/adversarial/ to broaden pipeline-validation coverage, adding additional payload sets intended to exercise cross-layer decoding/normalization chains, precision (false positives), and mixed obfuscation patterns.

Changes:

• Adds new prompt-, context-, normalization-evasion-, memory-, and cross-layer payload JSON libraries.
• Introduces a benign “false positive” payload case to validate non-overblocking behavior.
• Adds/updates the adversarial taxonomy README describing schema and coverage.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/adversarial/payloads/prompt_layer.json	Prompt-injection payloads, including multi-turn and a benign false-positive case
tests/adversarial/payloads/context_layer.json	Context-layer payloads (RAG/tool-output reinjection, context flooding)
tests/adversarial/payloads/normalization_evasion.json	Encoding/obfuscation payloads (homoglyph, base64, zero-width, leetspeak, mixed)
tests/adversarial/payloads/memory_layer.json	Memory/provenance attack payloads (poisoning, spoofing, replay)
tests/adversarial/payloads/cross_layer.json	Cross-layer payloads intended to become malicious post decoding/normalization
tests/adversarial/README.md	Documentation for payload organization, schema, and coverage matrix

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