REFACTOR: Make Translation/Variation/Persuasion inherit from LLMGenericTextConverter

[romanlutz]

What

Refactors TranslationConverter, VariationConverter, and PersuasionConverter to inherit from LLMGenericTextConverter instead of duplicating the build-conversation/send/return loop. Adds three small extensibility points to the base class so the three subclasses can be ~25-line thin wrappers.

Why

Three converters (~500 lines combined) each reimplemented:

• Conversation construction + system-prompt setup + send to target
• A bespoke retry policy (Translation: tenacity with max_retries/max_wait_time_in_seconds; Variation/Persuasion: @pyrit_json_retry)
• Response post-processing (Translation: .strip(); Variation: parse JSON list, take [0]; Persuasion: parse JSON, extract mutated_text)

The base class gains a _process_response hook and a unified retry helper that can produce both retry policies, so the duplication collapses cleanly.

Base-class additions (LLMGenericTextConverter)

• _process_response(response_text) -> str hook (default: identity)
• RETRY_EXCEPTIONS: tuple[type[BaseException], ...] class attribute (default () = no retry) + per-instance retry_exceptions constructor override
• max_retry_attempts: int | None and retry_wait_max_seconds: int | None constructor params for fixed-attempt + exponential-backoff policy; defaults give the same env-controlled, no-wait behavior as pyrit_json_retry
• **kwargs now also forwarded to user_prompt_template_with_objective rendering (in addition to system prompt)
• MessagePiece now built with original_value=raw_input, converted_value=templated_text (previously the raw input was lost when a user template was set)
• Input-type validation moved before set_system_prompt

Subclass changes

• TranslationConverter: inherits; passes both max_retry_attempts (=max_retries, default 3) and retry_wait_max_seconds (=max_wait_time_in_seconds, default 60) → behavior identical to before. F-string user prompt extracted into translation_user_prompt.yaml (byte-for-byte equivalent, regression-tested).
• VariationConverter: inherits; RETRY_EXCEPTIONS = (InvalidJsonException,); new variation_user_prompt.yaml for the per-call wrapper.
• PersuasionConverter: inherits; RETRY_EXCEPTIONS = (InvalidJsonException,); no user template (sends raw user prompt as before).

Compatibility

Deprecations (one release):

• VariationConverter.send_variation_prompt_async → public shim emitting DeprecationWarning; delegates to _send_with_retries_async
• PersuasionConverter.send_persuasion_prompt_async → same treatment

Observable bug-fix-style changes:

• VariationConverter: MessagePiece.original_value now stores the raw user input instead of the templated === begin === ... === end === wrapper. Matches Translation/Persuasion convention.
• TranslationConverter: set_system_prompt is no longer called on the target when input type is unsupported (validation moved before side effects).

Preserved:

• Translation max_retries=3, max_wait_time_in_seconds=60 defaults — fully functional, not deprecated
• Variation/Persuasion JSON retry semantics match pyrit_json_retry exactly (same exception type, same env-controlled attempt count via _DynamicStopAfterAttempt/RETRY_MAX_NUM_ATTEMPTS, same reraise=True, no wait between attempts)
• All persisted converter identifiers
• Translation user-prompt rendered text (byte-for-byte verified by regression test)
• All 8 existing LLMGenericTextConverter children (Tone, Tense, Noise, Denylist, Math, MaliciousQuestion, ScientificTranslation, ToxicSentenceGenerator) and RandomTranslationConverter's multiple inheritance

Tests

• 922 prompt_converter unit tests pass (added 15 new for base class hooks + 6 for refactored subclasses)
• 6,564 other unit tests pass — no cross-module regression
• Pre-commit clean (ruff, ty, yaml)