Fix default scalar values in command output

[RKS (rksharma-owg)]

Default integer and string command arguments currently become {"isDefault": true} in output. todict reads the marker classes' __dict__, losing the value the command returned.

Convert DefaultInt and DefaultStr to their built-in scalar types before object conversion. Regression coverage checks direct and nested results, built-in output types, and retention of the original default marker.

Fixes #215.

Validation on macOS, Python 3.12.13:

• The new regression fails for both default types before the fix.
• pytest: 246 passed, 2 subtests passed.
• License verification, flake8, and all 3 example tests pass.
• Pylint reports E1120 in unchanged knack/_win_vt.py:40; it also reproduces when linting that unchanged module alone.

AI assistance: Codex assisted with investigation, implementation, and local verification.

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