feat: add SameNetTraceMergeSolver pipeline phase

[Dannier314]

Adds a new pipeline phase SameNetTraceMergeSolver that merges trace segments belonging to the same electrical net when they run close together, reducing visual clutter in schematic output.

Changes

• New solver: SameNetTraceMergeSolver (groups traces by net, finds parallel overlapping segments, merges them)
• Integrated into pipeline after TraceCleanupSolver
• Downstream solvers (2nd NetLabelPlacementSolver, Example28Solver) prefer traces from the new solver

Algorithm

1. Group traces by net ID (dcConnNetId / globalConnNetId / userNetId)
2. For each group with >=2 traces, scan for parallel (H or V) segments within 0.5 units
3. Create a junction point at the overlap centroid and merge the paths
4. Iterate until no more mergeable pairs remain

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Project	Deployment	Actions	Updated (UTC)
schematic-trace-solver	Ready	Preview, Comment	May 14, 2026 9:04am

[Dannier314]

Implementation Notes

This implements the request from issue #29 to add a new pipeline phase that combines same-net trace segments that are close together.

How it works

1. Groups all traces by net ID (dcConnNetId / globalConnNetId / userNetId)
2. For each group with ≥2 traces, iterates over trace pairs
3. Checks each segment of trace A against each segment of trace B:
   • Horizontal segments: detects parallel (both horizontal) with Y-distance ≤ 0.5 AND overlapping X-range
   • Vertical segments: detects parallel (both vertical) with X-distance ≤ 0.5 AND overlapping Y-range
4. When parallel overlapping segments are found:
   • Creates a junction point at the centroid of the overlap
   • Reroutes both traces through the junction point using simplifyPath
   • Preserves mspPairId, pinId1, pinId2 from both original traces
5. Exits when no more mergeable pairs are found in an iteration

Integration

• Added to the pipeline immediately after TraceCleanupSolver (line 222-237 in pipeline def)
• Downstream solvers (netLabelPlacementSolver 2nd pass, example28Solver) fall back from SameNetTraceMergeSolver → TraceCleanupSolver → TraceLabelOverlapAvoidanceSolver

Testing

I wasn't able to run bun tests locally (missing bun in my environment). The code follows the same BaseSolver pattern as the other pipeline solvers. Would appreciate it if you could run bun test to verify.