refactor: sort import statements in docxtpl/

[waketzheng]

Description

1. Relocate the try ... except ImportError block in docxtpl/template.py to below the other import statements.
2. Reorder imports with isort (run uvx isort docxtpl).

This is based on PR #647.
Diff: waketzheng/python-docx-template@remove-noqa...sort-imports

[CAOShurong]

I independently reviewed and tested the exact head f583ed3428af05eab158960cb06f382c193ebec4.

• All 37 test scripts passed when run directly with the review environment's Python interpreter.
• flake8 and git diff --check passed, and both the sdist and wheel built successfully.
• From clean wheel installs, from docxtpl import * excluded Subdoc when docxcompose was absent and included it when the optional dependency was installed.
• A normal template rendered and reopened successfully from the installed wheel; the optional-dependency environment also rendered and reopened a document containing a generated subdocument.
• The 14 upstream test/codestyle checks are green.

The import-only changes preserve the optional dependency behavior and look correct to me.

OpenAI Codex assisted with the exact-head test matrix and diff review. I personally checked the commands, outputs, installed-wheel behavior, and this approval.