REFACTOR: Promote token-smuggling & misc converter defaults to ClassVar

Part of the ongoing class-constants audit (see #1964, #1965). Pure structural rename — no value or behaviour changes.

What changed

Promotes hard-coded __init__ defaults onto the owning class as ClassVar constants, using the sentinel-default pattern documented in the audit kickoff so subclasses can inherit the default without restating it.

pyrit/prompt_converter/token_smuggling/

The four-class SmugglerConverter family all shared action: Literal["encode", "decode"] = "encode". The default now lives once on the base:

class SmugglerConverter(PromptConverter, abc.ABC):
    DEFAULT_ACTION: ClassVar[Literal["encode", "decode"]] = "encode"

    def __init__(self, action: Literal["encode", "decode"] | None = None) -> None:
        if action is None:
            action = self.DEFAULT_ACTION
        ...

The three subclasses (AsciiSmugglerConverter, SneakyBitsSmugglerConverter, VariationSelectorSmugglerConverter) now accept action: Literal["encode", "decode"] | None = None and delegate resolution to the base via super().__init__(action=action). Their existing _brick_legacy_init = True opt-out (positional-arg deprecation grandfathering, scheduled for removal in 0.16.0) is preserved unchanged.

pyrit/prompt_converter/unicode_sub_converter.py

UnicodeSubstitutionConverter had a lone hard-coded start_value: int = 0xE0000. Promoted to DEFAULT_START_VALUE: ClassVar[int] = 0xE0000 and the constructor uses the same sentinel pattern.

Conventions followed

• ClassVar[T] annotation on every promoted constant.
• PEP 604 unions (X | None) for the sentinel parameter type.
• Constants placed near the top of the class body (per the style-guide method-ordering checklist).
• Docstrings updated to reference the DEFAULT_* constant by name.
• _brick_legacy_init and positional signatures preserved for the smuggler family (no signature changes).

Verification

uv run --link-mode=copy ruff check pyrit/prompt_converter/token_smuggling/ pyrit/prompt_converter/unicode_sub_converter.py
uv run --link-mode=copy ty check pyrit/prompt_converter/token_smuggling/ pyrit/prompt_converter/unicode_sub_converter.py
uv run --link-mode=copy pytest tests/unit/prompt_converter/ -x --no-header -q

All green — 1012 passed, 38 skipped (no test changes needed; the public default is unchanged).