[WIP] Upgrade to Python 3.12 and ONNX 1.21.0

[auphelia]

WIP: currently in testing and some outstanding issues identified:

• XRT 2024.2 for Ubuntu 24.04 - Need to verify availability and download location
• Which Vivado version are now compatible
• ONNXRuntime MaxPool bug - onnxruntime 1.26 has a regression where MaxPool with ceil_mode=1 and padding produces incorrect output shapes (see test_maxpool_nhwc.py failure). Shape inference computes correct output but execution kernel produces wrong dimensions.

Summary

Upgrades FINN to Python 3.12 and ONNX 1.21.0 to address a critical security vulnerability (CVE: ExternalDataInfo attribute injection) while maintaining compatibility across all dependencies.

Motivation

• Security: Dependabot alert recommending ONNX upgrade from 1.17.0 → 1.21.0
• Compatibility: QONNX constrains ONNX ≤1.17 for Python <3.11, requiring Python upgrade to unlock newer ONNX versions
• Ecosystem: Python 3.12 (Oct 2023) provides mature package support and long-term stability

Key Changes

• Python 3.10 → 3.12
• Ubuntu 22.04 → 24.04 (noble)
• Implemented PEP 668 compliance (--break-system-packages for Docker) and fixed typing_extensions conflict in Docker build
• onnx: 1.17.0 → 1.21.0
• onnxruntime: 1.18.1 → 1.24.0
• Updated 15+ packages for Python 3.12 compatibility
• Updated ReadTheDocs and GHAs to ubuntu-24.04
• Removed deprecated mapping import from onnx module (ONNX 1.21.0 compatibility)