Fix: add missing library dependencies to flake

[Kaweees]

This adds two missing library dependencies (gfortran.cc.lib and libidn2) to the flake configuration. These packages are needed to run on the Jetson platform. Related: #1229 and #980

[greptile-apps]

Greptile Overview

Greptile Summary

This PR adds two missing library dependencies to the Nix flake configuration:

• gfortran.cc.lib: Required for scientific computing packages like scipy and numpy that need Fortran libraries for optimized linear algebra operations
• libidn2: Required for internationalized domain name support in networking libraries

Both dependencies are correctly configured with ldLibraryGroup=true flags to ensure they're added to the LD_LIBRARY_PATH. The gfortran.cc.lib is placed alongside other compiler libraries in the "Core shell & utils" section, while libidn2 is placed in the "Open3D & build-time" section near other image/media libraries.

Confidence Score: 5/5

• Safe to merge - adds only standard library dependencies without any code changes
• The changes are minimal and low-risk, adding only two well-known library dependencies to the Nix flake. Both libraries are correctly configured with appropriate flags and placed in logical sections. No code logic is modified, only build configuration.
• No files require special attention

Important Files Changed

Filename	Overview
flake.nix	Added gfortran.cc.lib and libidn2 library dependencies with correct flags

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