fix: copy order actions in prefetch so querysets can be re-executed

[moneebullah25]

Fixes #1818

LoadNode mutated the shared OrderAction objects (is_source_model_order, table_prefix) while building prefetch queries, so executing the same queryset a second time with prefetch_related + order_by on a related field gave wrong results. The order action is now copied before it is modified.

Changes:

• ormar/queryset/queries/prefetch_query.py: copy.copy the order action before mutating it.
• tests/test_relations/test_prefetch_related.py: regression test that runs the same queryset twice.

Checks run:

• ruff format --check and ruff check on the changed files: clean

• mypy --ignore-missing-imports on the changed files: no issues

• pytest tests/test_relations/test_prefetch_related.py tests/test_queries: 112 passed

• Tests added for the change

• Linting and type checks run on changed files

• Docs updated (not applicable)