Add 8 IC subcircuits: LM129, REF102, TL317, LM236, MC1413, ULN2004, SN75468, SN7406

[hardikgarg2006]

Related Issues

N/A

Purpose

This PR adds 8 IC subcircuits to the SubcircuitLibrary, expanding available components for eSim users.

Approach

Each IC was designed as a schematic in eSim, converted to an Ngspice subcircuit, and tested via simulation to verify correct behavior against datasheet specifications.

ICs Included

1. LM129 — Precision Voltage Reference
2. REF102 — Precision Voltage Reference
3. TL317 — Adjustable Voltage Regulator
4. LM236 — Precision Voltage Reference Diode
5. MC1413 — Darlington Transistor Array
6. ULN2004 — Darlington Transistor Array
7. SN75468 — Darlington Transistor Array
8. SN7406 — Hex Inverter Buffer/Driver

Checklist

• 1 PR containing all my ICs
• 1 commit per IC with descriptive commit messages
• Included README.md with description for each IC