feat(parsers): add IriusRisk threat model CSV parser

[skywalke34]

Description

New parser for IriusRisk threat model CSV exports. IriusRisk is a threat
modeling and risk management platform. The parser:

• Parses CSV exports from IriusRisk threat model views
• Maps all 14 CSV fields to DefectDojo Finding fields
• Maps IriusRisk risk levels (Critical/High/Medium/Low/Very low) to
  DefectDojo severity levels
• Extracts CWE numbers from MITRE references when present
• Generates SHA-256 unique IDs for deduplication across reimports
• Sets findings inactive when Current Risk is "Very low" (fully mitigated)

Test results

23 unit tests covering:

• Empty file, single finding, and multiple findings parsing
• All 5 severity levels (Critical, High, Medium, Low, Info)
• Title truncation, component name extraction, description construction
• Mitigation field mapping, active/inactive status logic
• Unique ID generation and consistency
• CWE extraction from MITRE references
• STRIDE-LM and owner field handling

Documentation

Parser documentation at docs/content/supported_tools/parsers/file/iriusrisk.md
with export instructions, complete field mapping table, severity mapping, and
special processing notes.

Checklist

• Rebased against the very latest dev
• Submitted against dev branch
• Meaningful PR name
• Code is flake8/ruff compliant
• Code is Python 3.13 compliant
• Documentation included
• No model changes, no migrations needed
• Unit tests included (23 tests)
• Label: Import Scans

Authored by T. Walker - DefectDojo