Preserve native curved PCB routes

[ShiboSoftwareDev]

Summary

• import partial Altium copper arcs as one Circuit JSON route segment with standard bulge curvature instead of many straight chords
• export curved route segments as native Altium Arc records while retaining straight Track output for ordinary segments
• preserve clockwise and counterclockwise geometry, net, layer, and width
• pin the exact native Arc writer from Serialize native PCB arcs altiumts#102

Schema dependency: tscircuit/circuit-json#744
Writer dependency: tscircuit/altiumts#102

Real-board verification

• NodeMCU ESP-12 contains 214 netted copper arcs
• source import: 214 curved traces
• binary Altium round trip: 214 curved traces
• updated the real-board side-by-side snapshot

Tests

• bun run format:check
• bun run typecheck
• bun test --max-concurrency 1 (25 pass, 0 fail)