fix: propagate input stream in Command.call() for interactive questions

[binggao1230]

Problem

When a command uses call() to invoke another command that contains interactive questions (confirm, ask, choice), the callee crashes with:

AttributeError: 'NoneType' object has no attribute 'readline'

Root cause: call() constructs a fresh StringInput whose _stream defaults to None, but never copies the parent IO's stream. When the callee calls:

confirm() → Question.ask() → io.read_line() → input.read_line() → self._stream.readline()

self._stream is None, causing the crash.

Fix

Propagate self._io.input.stream to the new StringInput before passing it to _run_command:

string_input = StringInput(args or "")
string_input.set_stream(self._io.input.stream)

Test

Added test_call_propagates_stream_for_confirm which exercises a caller→callee chain where the callee uses confirm(), providing inputs="yes\n" through ApplicationTester. Before this fix the test raises AttributeError; after it passes.

Fixes #333

---

This pull request was prepared with the assistance of AI, under my direction and review.

[binggao1230]

Pushed a follow-up for the red checks:

• added news/333.bugfix.md for the bug fix
• ran pre-commit run --all-files; it reformatted the new Command.call() return line, and the follow-up includes that formatting change

Verification:

• uv run --with towncrier towncrier check --compare-with origin/main -> found news/333.bugfix.md
• uv run --with pre-commit pre-commit run --all-files -> passed
• uv run --with pytest python -m pytest tests/commands/test_command.py -q -> 6 passed
• git diff --check --cached -> passed before commit