REFACTOR: Promote printer dimension defaults (width / blur_radius / font_size) to ClassVar on printer base

[Roman Lutz (romanlutz)]

Summary

Promotes printer dimension defaults (width = 100, blur_radius = 20) from per-constructor hard-coded literals to ClassVar[int] attributes on PrinterBase in pyrit/output/base.py:

• DEFAULT_WIDTH: ClassVar[int] = 100
• DEFAULT_BLUR_RADIUS: ClassVar[int] = 20

Subclass constructors now use the sentinel-default pattern (width: int | None = None, resolved to self.DEFAULT_WIDTH at the point of consumption). Docstrings reference DEFAULT_WIDTH / DEFAULT_BLUR_RADIUS (with the value in parentheses).

This is part of the ongoing constants-audit cleanup (continuation of the pattern established in #1964 and #1965).

Scope

Touched only pyrit/output/:

• base.py — added DEFAULT_WIDTH and DEFAULT_BLUR_RADIUS ClassVars on PrinterBase.
• attack_result/pretty.py, attack_result/markdown.py
• conversation/pretty.py, conversation/markdown.py
• scenario_result/pretty.py
• score/pretty.py
• helpers.py — output_attack_async and output_conversation_async now take blur_radius: int | None = None and forward None to the printer (printer sentinels resolve the default).

Notes

• The kickoff doc mentioned a font_size = 15 default in printer files, but there are no font_size references anywhere in pyrit/output/. (The font_size = 15 hits in the repo are in pyrit/prompt_converter/, out of scope for this PR.) Only DEFAULT_WIDTH and DEFAULT_BLUR_RADIUS are promoted here.
• All width and blur_radius defaults in pyrit/output/ were already consistent (100 and 20 respectively) — no diverging values to preserve.

No value changes. No behaviour changes.

Verified: ruff check pyrit/output/, ty check pyrit/output/, pytest tests/unit/output/ (173 passed).

[Roman Lutz (romanlutz)]

Closing per maintainer feedback on the constants-audit work.

This PR introduced the sentinel-default pattern (changing x: T = <literal> into x: T | None = None + if x is None: x = self.DEFAULT_X) which widens the public API signature. The preference is to keep constants inside their owning class (Track A — see #1964, #1965, #1972, #1973, #1974, #1975) but not to promote hard-coded single-use defaults via a None-sentinel.

Branch left intact in case any portion is worth cherry-picking later.