requirements.txt includes apturl which is not pip-installable and breaks setup on Windows/macOS

[kunalsanga]

Description

While trying to set up the Grid-based strong lensing SISR project on a clean
Windows environment, pip install -r requirements.txt fails due to the
dependency apturl==0.5.2.

apturl is an OS-level Ubuntu package and is not available via pip, which makes
the current setup non-functional on Windows and macOS.

Steps to reproduce

1. Create a fresh Python virtual environment
2. Run pip install -r requirements.txt

Observed behavior

Installation fails with:
ERROR: No matching distribution found for apturl==0.5.2

Expected behavior

A new contributor should be able to install dependencies via pip on a
cross-platform environment.

Proposed fix

• Remove apturl from requirements.txt
• Document OS-specific/system dependencies separately if required
• Optionally split dependencies into:
  • core (pip-installable)
  • system/optional

I’d be happy to submit a PR to address this.