refactor: consolidate _log_git_stderr_errors into models/_git_utils.py

[Copilot]

_log_git_stderr_errors lived in subprocess_utils.py rather than models/_git_utils.py, the established home for git helpers. This scattered git utilities across two modules.

Changes

• models/_git_utils.py — added _log_git_stderr_errors (with loguru import)
• models/template.py — merged imports: from rhiza.models._git_utils import _log_git_stderr_errors, _normalize_to_list
• commands/_sync_helpers.py — updated import source from subprocess_utils → models._git_utils
• tests/test_commands/test_sync.py — updated import and mock patch target to rhiza.models._git_utils.logger
• subprocess_utils.py — deleted (now empty)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Duplication</issue_title>
<issue_description>2. 🔁 Deduplicate _log_git_stderr_errors

Files: src/rhiza/models/_git_utils.py and src/rhiza/commands/_sync_helpers.py

_log_git_stderr_errors is defined in both models/_git_utils.py and commands/_sync_helpers.py. Remove the copy in _sync_helpers.py and import it from rhiza.models._git_utils (or rhiza.models) — which is already the canonical home for git helpers.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Duplication #408

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