String parser fails for led and diode with imperial sizes (e.g., led0402, diode0603)

[claw-explorer]

Summary

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:

Error: Could not determine required pad dimensions (p, pw, ph)

Root Cause

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

if (prop === "res" || prop === "cap") {
  target.imperial = v  // correctly sets imperial size
} else {
  target.num_pins = Number.parseFloat(v)  // incorrectly treats as pin count
}

So led0402 gets parsed as { fn: "led", num_pins: 402 } instead of { fn: "led", imperial: "0402" }.

Reproduction

import { fp } from "@tscircuit/footprinter"

// These work:
fp.string("res0402").circuitJson()  // ✓
fp.string("cap0603").circuitJson()  // ✓
fp().led().imperial("0402").circuitJson()  // ✓ (builder API works)

// These fail:
fp.string("led0402").circuitJson()    // ✗ Error
fp.string("led0603").circuitJson()    // ✗ Error
fp.string("diode0402").circuitJson()  // ✗ Error
fp.string("diode0805").circuitJson()  // ✗ Error

Expected Behavior

All four passive footprint types (res, cap, led, diode) should support the same <name><imperial_size> string syntax, since they all delegate to the same passive() function.

Impact

Users cannot use standard footprint strings for LED and diode passive packages. They must use the builder API instead, which is inconsistent with the res/cap behavior.

[chengyixu]

/attempt #562

Root cause identified and fix ready in PR #565.

The proxy handler in footprinter.ts only treated res and cap as passives supporting imperial/metric size codes. led and diode use the same passive() helper, so a one-line fix extending the condition resolves it. Also widened the diode() parameter type to PassiveDef to match led. Added 8 regression tests. All 392 existing tests still pass.