Implement UTDFN-4-EP(1x1) footprint

[ChandraDvitiyah]

Summary

• add a UTDFN footprint generator backed by the existing VSON pad layout
• normalize KiCad-style UTDFN-4-EP(1x1) strings to the new utdfn4_w1mm_h1mm_ep footprint
• cover the alias, exposed-pad output, and SVG snapshot

Fixes #183

Testing

• npx biome check src/fn/utdfn.ts src/fn/index.ts src/footprinter.ts src/helpers/zod/AnyFootprinterDefinitionOutput.ts tests/utdfn.test.ts tests/__snapshots__/utdfn4_w1mm_h1mm_ep.snap.svg
• npm run build
• node -e 'import("./dist/index.js").then(({fp})=>{const cj=fp.string("UTDFN-4-EP(1x1)").circuitJson(); const pads=cj.filter(e=>e.type==="pcb_smtpad"); const same=JSON.stringify(cj)===JSON.stringify(fp.string("utdfn4_w1mm_h1mm_ep").circuitJson()); console.log({pads:pads.length, sameAlias:same, thermalPad:pads[pads.length-1]})})'

Note: bun is not installed in this environment, so I could not run bun test. A full npx tsc --noEmit currently fails on existing test typing issues unrelated to this change.