fix: string parser now handles led and diode imperial sizes

[64johnlee]

Summary

Fix Issue #562 - String parser fails for led and diode with imperial sizes.

Problem: The string parser does not correctly handle imperial/metric size codes for led and diode footprints. While res0402 and cap0603 work correctly, led0402 and diode0603 throw an error.

Root Cause: In src/footprinter.ts, the proxy handler only recognizes res and cap as passive footprints that use imperial/metric sizing.

Solution: Added led and diode to the list of passive footprints that use imperial sizing.

// Before
if (prop === "res" || prop === "cap") {

// After
if (prop === "res" || prop === "cap" || prop === "led" || prop === "diode") {

Testing

• led0402 now correctly parses as { fn: "led", imperial: "0402" }
• diode0603 now correctly parses as { fn: "diode", imperial: "0603" }