Initial project structure for spice2wireviz

SPICE netlist to WireViz YAML converter with:
- Custom lightweight netlist parser (.net/.cir/.sp)
- Single-module mapper (subcircuit external interface)
- Inter-module mapper (multi-board wiring)
- Filter engine with glob patterns
- Click CLI with auto-detection, inspection commands
- Optional .asc parser via spicelib
- Comprehensive test suite with fixtures

tests/fixtures/multi_board.net

@@ -0,0 +1,27 @@
+* Multi-board system: power supply, amplifier, and I/O board
+* Demonstrates inter-module wiring
+
+.subckt power_supply VCC GND
+J1 AC_IN AC_GND AC_INLET
+.ends power_supply
+
+.subckt amplifier VIN GND VOUT
+R1 VIN N001 10k
+C1 N001 GND 100n
+J1 VIN GND INPUT_CONN
+TP1 VOUT
+.ends amplifier
+
+.subckt io_board SIG_IN SIG_OUT GND CTRL
+J1 SIG_IN SIG_OUT DB9_CONN
+J2 CTRL GND CTRL_CONN
+.ends io_board
+
+* Top-level instantiation
+X1 VCC GND power_supply
+X2 VCC GND AUDIO_OUT amplifier
+X3 AUDIO_OUT CTRL_SIG GND ENABLE io_board
+
+* Top-level connectors
+J_CHASSIS GND EARTH chassis_gnd
+TP_VCC VCC