feat: make max options displayed configurable per question (closes #80)

[SAY-5]

Closes #80.

Adds a per-question max_options_displayed_at_once parameter to List and Checkbox questions. When unset (default), the existing 13-row window is preserved; when set to a positive integer it overrides the visible window size, letting users browse longer choice lists without truncation.

Hmm, I think we would accept PR with this proposal. — @AuHau, #80 (comment)

The renderers (_list.py, _checkbox.py) read the value through a property on the render class, so the module-level MAX_OPTIONS_DISPLAYED_AT_ONCE constant continues to define the default and other consumers are unaffected.

Tests:

• test_max_options_displayed_at_once_shows_more_choices (List, Checkbox): renders 40 choices with max_options_displayed_at_once=25 and asserts choices 0-24 are visible while choice 25 is windowed out.
• test_max_options_displayed_at_once_default_unchanged (List, Checkbox): confirms the default 13-row window still applies.
• Both render tests fail with TypeError: ... got an unexpected keyword argument 'max_options_displayed_at_once' if the source change is reverted.
• Full tests/integration/console_render/test_list.py + test_checkbox.py + tests/unit suite: 98 passed, 2 skipped locally on Python 3.11.

Docs: added a max_options_displayed_at_once section to docs/usage.md.