Error pcb courtyard overlap error even if they are on different layers

[rushabhcodes]

Package code to reproduce

Error

pcb_courtyard_overlap_error: Courtyard of R1 overlaps with courtyard of R2
@tscircuit/eval@0.0.652
@tscircuit/core@0.0.1125

[ysdy823]

The root cause is in the @tscircuit/checks package — the courtyard overlap checker doesn't compare layers before reporting overlap.

Fix submitted: tscircuit/checks#130

The change adds a layer comparison in checkCourtyardOverlap.ts so courtyards on different PCB layers (top vs bottom) are not flagged as overlapping.