fix: escape % in class-variable comments so argparse help formatting does not crash (#183)

[patchwright]

Problem

Fixes #183. A % in a class-variable comment crashes Tap (TypeError: %c requires int or char on Python <3.14; ValueError from _check_help on 3.14+). Confirmed on main HEAD fd2e8416.

Root cause

Tap._add_argument appends the extracted comment to the argparse help string verbatim (kwargs["help"] += " " + comment). argparse %-formats every help string (help_string % params), so a literal % in the comment is read as a format spec and crashes.

Fix

Escape % to %% (the standard argparse escape for a literal percent) when appending the comment. One source line in src/tap/tap.py; no API changes.

How to test

# saved as repro.py
from tap import Tap

class MyTap(Tap):
    percent: int = 100  # The % chance this will break

MyTap().format_help()

$ python repro.py
Traceback (most recent call last):
  ...
  File ".../argparse.py", line 640, in _expand_help
    return self._get_help_string(action) % params
TypeError: %c requires int or char

With this PR it returns the help text with the comment intact. Added test_comment_with_percent in tests/test_integration.py, verified to fail on unpatched main and pass with the fix.

Backward compatibility

No breaking changes. Comments render identically; %% is collapsed back to % by argparse's own formatting.

---

Assisted-by: Claude (code generation, reviewed and tested locally)

[martinjm97]

This test would benefit from a full string match to ensure the parse is actually "The % chance this will break" and not mangled.

[martinjm97]

Thank you for your contribution to Tap!

--JK