Fix Ruff linting failures on solar calibration branch

[harrison-lccc]

Task summary
Resolve the Ruff linting failures currently blocking the solar calibration branch.

Why this task is needed
The branch cannot be merged because the lint checks report two errors.

Proposed implementation

• Sort and format imports in rencal/calibration/solar/__init__.py.
• Remove the unused quad import from rencal/calibration/solar/solar_calibrator.py.
• Run uv run ruff check . to verify the fixes.

Acceptance criteria

• rencal/calibration/solar/__init__.py passes Ruff import sorting checks.
• rencal/calibration/solar/solar_calibrator.py has no unused imports.
• uv run ruff check . completes successfully.
• The task remains standalone and is not linked to another issue.

Additional context
Detected errors:

• I001: import block is unsorted or unformatted.
• F401: scipy.integrate.quad imported but unused.