Remove all pre-1.0.0 PyRIT-internal deprecations (0.16.0/0.17.0)

[romanlutz]

Remove all pre-1.0.0 PyRIT-internal deprecations (0.16.0 / 0.17.0 / stale 0.18.0)

PyRIT's last release was 0.14.0; the next is 1.0.0. Every PyRIT-owned API that emitted a
DeprecationWarning slated for removal in 0.16.0 or 0.17.0 is now fully removed — both the
deprecated code paths/shims and every internal caller (pyrit/, tests/, doc/) migrated to
the replacement API. The single 0.18.0 deprecation (ScenarioCompositeStrategy) is also removed:
with versioning jumping 0.14 -> 1.0.0 there is no 0.18.0 release, so its target is stale.

What changed (by subsystem)

• models — dropped to_dict/from_dict/validate/get_all_values/flatten_to_message_pieces/
  duplicate_message/set_*_not_in_database, positional Message(...) / skip_validation, the
  MessagePiece(labels=...) constructor warning, and set_sha256_* helpers → model_dump/
  model_validate / module functions / pyrit.memory.storage.serializers.
• memory — removed StorageIO/DataTypeSerializer/data-url sync aliases, get_conversation, and
  attack_id= params → get_conversation_messages / conversation_id= via get_attack_results.
• labels / attack_identifier — removed the deprecated labels= and attack_identifier= plumbing
  across normalizer, targets, mappers, attack service, and multi-turn/promptgen executors (the
  MessagePiece.labels field stays; only the deprecated kwargs are gone).
• common / identifiers / setup — deleted the pyrit.identifiers shim package and the
  pyrit.common.{parameter,data_url_converter,question_answer_helpers} module shims.
• datasets — removed fetch_dataset sync + legacy-subclass path and the remote-dataset split=
  kwargs.
• auth / message-normalizer — dropped the sync aliases (get_claims, get_sas_token,
  apply_system_message_behavior, ...).
• converters / targets — grandfathered __init__s are now keyword-only; removed
  send_persuasion_prompt_async/send_variation_prompt_async, PromptChatTarget,
  TextTarget.import_scores_from_csv, gandalf check_password, and the realtime deprecations.
• output printers — removed deprecated print_*/output_conversation_async methods and the
  score/executor.attack/scenario printer module shims.
• executors / scenarios — removed system_prompt_path, PrependedConversationConfig
  non-chat deprecations, AtomicAttack(attack=...), Scenario(include_default_baseline=...),
  factory adversarial_config, scenario include_baseline ctor kwargs, and
  ScenarioCompositeStrategy (→ FoundryComposite).
• DatasetConfiguration (post-inventory) — main recently added six DatasetConfiguration
  legacy getters (get_seed_groups, get_all_seed_groups, get_seed_attack_groups,
  get_all_seed_attack_groups, get_default_dataset_names, get_all_seeds) marked for 0.17.0.
  Since 0.17.0 will never ship, these are removed too and all callers migrated to the async
  DatasetAttackConfiguration API (get_attack_groups_by_dataset_async / dataset_names).

Verification

• uv run -m pytest -n 4 --dist=loadfile tests/unit → 9873 passed, 120 skipped, 0 failures.
• 0 PyRIT-owned DeprecationWarnings remain. The only warnings left are third-party
  (StarletteDeprecationWarning: HTTP_422) and a test-only asyncio.iscoroutinefunction note,
  both out of scope for this PR.
• Repo-wide grep confirms no removed_in="0.16.0"/"0.17.0"/"0.18.0" markers remain in pyrit/.
• ruff format, ruff check, and ty all pass (enforced via pre-commit).