fix(schema): tenthmil no longer emits "NaNmil" for missing pad coordinate/size fields

[bnuckols13]

Problem

tenthmil (used by PadSchema, RectSchema, and TextSchema for coordinates and sizes) is .optional(), but its transform ran `${Number.parseFloat(n) * 10}mil` on every non-unit value. When a field is undefined — which happens when a short/variant EasyEDA pad string omits a trailing field such as holeRadius — Number.parseFloat(undefined) is NaN, producing the nonsensical unit string "NaNmil".

Downstream in convert-easyeda-json-to-tscircuit-soup-json.ts, a "NaNmil" holeRadius makes mil2mm(pad.holeRadius) !== 0 true, so the pad is treated as a plated hole and emits NaN geometry — surfacing as "NaNmm" in the generated component (the exact string the convert-to-ts tests guard against with expect(result).not.toContain("NaNmm")).

Fix

Guard the parse: fall back to 0 when Number.parseFloat yields NaN, matching the safeNumber(0) convention already used in this file. A missing holeRadius now reads as 0 (an SMT pad) instead of NaN geometry.

Repro

PadSchema.parse({ type: "PAD", shape: "ELLIPSE", center: { x: 100, y: 200 },
                  width: 60, height: 60, layermask: 1, number: 1, plated: false }) // holeRadius omitted

• before: holeRadius: "NaNmil"
• after: holeRadius: "0mil"

Tests

Adds tests/parse-tests/pad-tenthmil-nan.test.ts (missing field → no NaN leak; valid inputs preserved). Existing suites stay green: parse-tests 15, convert-to-soup-tests 21, convert-to-ts 59.