Add tests for defaults-only, programmatic, and VCS copier generation

[buddingengineers12345]

Coverage gaps addressed

The existing tests covered copier copy . <dest> --data project_name=... but did not cover the example scenarios:

• defaults-only CLI generation (--defaults without --data)
• programmatic generation via copier.run_copy(...)
• VCS-style template sources (git URL / gh: / gl: style)

What changed

• Added three new tests in tests/test_template.py:
  • defaults-only CLI: copier copy . <dest> --trust --defaults --skip-tasks
  • programmatic local path: run_copy(".", <dest>, defaults=True, unsafe=True, skip_tasks=True)
  • VCS-style source (network-free): create a temporary git repo and run copier copy git+file://... <dest> --trust --defaults --skip-tasks

Why this approach

• Uses --skip-tasks to keep CI fast/stable while still exercising Copier's rendering + source acquisition code paths.
• Uses git+file:// to emulate the VCS code path without relying on external network.

Verification

• just ci passes