* feat: remove cells2, cells_fixed, cni — bump to 2.0.0
- Delete ihp/cells2 (CNI-based PyCell reference implementations)
- Delete ihp/cells_fixed (deprecated fixed-GDS wrapper cells)
- Delete cni/ runtime package (only required by cells2)
- Delete tests/test_xor_transistors.py (XOR tests against cells2)
- Remove cells2/cni references from tech.py, pyproject.toml, README, CONTRIBUTING
- Move CuPillarPad_fixed → CuPillarPad in ihp/cells/bondpads.py
- Bump version 0.3.0 → 2.0.0
* fix: remove cells2/cells_fixed imports from write_cells.py