fix: preserve schematic pin numbers for named footprint pads

[GokulPandi-M]

Motivation

Some EasyEDA parts use a functional name for a footprint pad but a numeric pin for the same schematic terminal. For C393941, the symbol defines card detect as pin 9 / CD while the footprint names the pad CD. The converter created a new pin 14, so users connecting pin 9 would not reach the physical card-detect pad.

Changes

• Map a named pad to a unique, otherwise-missing numeric schematic pin with the same label.
• Keep exact numeric matches as the primary behavior.
• Leave ambiguous labels and already-used numeric pads unchanged.
• Update the C393941 output assertions and schematic snapshot to show CD on pin 9.

Scope

The missing CD/DAT3 display name on pin 2 is a separate slash-label parsing issue covered by #501 and is intentionally not mixed into this fix. Pins 10-13 have only numeric names in the source data.

Verification

• 204 tests pass, including the existing C7203002 named-test-pad regression
• Typecheck passes
• Format check passes
• Build passes

Follow-up fix for #530.

[ShiboSoftwareDev]

we have a policy now of only fixing issues found on real circuits, I believe I already told you not sure

[GokulPandi-M]

@ShiboSoftwareDev Sorry, I should have mentioned the context earlier. I found this issue while checking the component for a hub board I’m building. I’ll include that context in future PRs so that you may get to know!!