Fix standalone import failure in DataTables utilities

[Copilot]

The Python 3.10 Actions job failed during test collection because sequana_report still relied on sequana.lazy at import time. In the standalone package context used by CI, that dependency is not installed, so importing the DataTables utilities raised ModuleNotFoundError.

• Import compatibility

  • Update sequana_report.utils.datatables_js to use sequana.lazy.pandas when available, with a direct pandas fallback when the parent sequana package is absent.
  • This keeps compatibility with the Sequana runtime while allowing sequana_report to import cleanly as an independent package.

• Regression coverage

  • Add a focused import regression test that spawns a fresh interpreter and imports sequana_report.utils.datatables_js.
  • This covers the same failure mode seen in CI: package import in an environment where sequana is not present.

• Behavioral impact

  • No DataTable API changes.
  • Scope is limited to import-time dependency handling for standalone installs.

try:
    from sequana.lazy import pandas as pd
except ImportError:
    import pandas as pd