DRC idea: I2C topology check

Description

When running DRC with nets named i2c-*, netlist topologies other than a string of point to point nodes could usefully generate an error.

For example, when building a small breakout for multiple sensors, it makes sense to string multidrop buses like I2C from the off-board connector through a series of copper traces and pads. Rarely is it a good idea to embrace alternate topologies where the netlist splits in star or similar fashion.

Steps to reproduce

1. Create a net named 'I2C*'
2. Make an invalid (non I2C-like topology)
3. DRC will pass.
4. DRC should fail.

KiCad Version

Application: KiCad PCB Editor arm64 on arm64

Version: 9.0.7, release build

Libraries:
	wxWidgets 3.2.8
	FreeType 2.13.3
	HarfBuzz 10.1.0
	FontConfig 2.15.0
	libcurl/8.7.1 (SecureTransport) LibreSSL/3.3.6 zlib/1.2.12 nghttp2/1.67.1

Platform: macOS Version 26.2 (Build 25C56), 64 bit, Little endian, wxMac
OpenGL: Apple, Apple M4, 2.1 Metal - 90.5

Build Info:
	Date: Jan  1 2026 21:36:00
	wxWidgets: 3.2.8 (wchar_t,wx containers)
	Boost: 1.87.0
	OCC: 7.8.1
	Curl: 8.7.1
	ngspice: 44.2
	Compiler: Clang 16.0.0 with C++ ABI 1002
	KICAD_IPC_API=ON