FEAT: Adding useless descriptions to Techniques

[rlundeen2]

Description

Adds an optional description field to attack technique factories, so each technique in pyrit/setup carries a concise summary of what it does.

• New keyword-only description: str | None = None on AttackTechniqueFactory.__init__ (and forwarded through with_simulated_conversation), exposed via a description property.
• Deliberately excluded from _build_identifier — it's decorative metadata and must not change a technique's behavioral identity hash.
• Populated a concise description for every technique in the core, extra, and airt catalogs.

Right now these are informational only (as the title says, currently useless / decorative); a follow-up could surface them in registry/CLI listings.

Tests

• Added 5 cases in test_attack_technique_factory.py: default None, stored value, forwarding through with_simulated_conversation, and a guard that description does not affect the identifier hash.
• test_attack_technique_factory.py (62 passed), test_technique_initializer.py (46 passed), ruff clean.

Co-authored-by: Copilot App 223556219+Copilot@users.noreply.github.com