Add patent scan plugin with CLI support and extended detection tests

[dikshaa2909]

Fixes #4510

Summary

This PR adds a new Patent Scan Plugin to detect patent references and patent numbers in scanned files.

The implementation follows existing ScanCode plugin architecture and integrates with the CLI, API, and JSON output.

---

Features

• New CLI flag: --patent
• Threshold option: --max-patent (default: 50, 0 for no limit)
• Detection of:
  • Patent numbers (US, EP, WO, JP, CN, KR, GB, IN)
  • Formats like:
    • US Patent 8,123,456 B2
    • US20190012345A1
    • EP1234567B1
    • WO 2019/123456
  • Patent keywords:
    • patent pending
    • patented
    • patent application
    • patent number
• Word-boundary checks to avoid false positives (e.g., unpatented)
• Deduplication and threshold enforcement
• Structured output under patent_detections

---

Implementation

• Detection logic: src/cluecode/patents.py
• CLI plugin: src/cluecode/plugin_patent.py
• API integration: get_patents() in scancode.api
• Registered via setup.cfg

---

Tests

Added tests covering:

• Basic detection
• International formats
• Keyword detection
• No false positives
• Threshold behavior

Tests pass locally and in Docker.

---

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled and linked to issue
• Tests pass locally
• Feature branch used
• Updated documentation (if required)
• Updated CHANGELOG (if required)

Signed-off-by: dikshaa2909 dikshadeware@gmail.com