Add SPDIP-28 footprint with string aliases and SVG tests

[ikoomm]

Closes #180.

Adds SPDIP-28 / spdip28 and the typed fp().spdip() builder, defaulting to 28 pins on a 7.62 mm row grid with 2.54 mm pitch. Reuses the existing DIP generator for numbered plated holes, pin-one marking, silkscreen and courtyard. Includes documentation, six regression tests and two SVG snapshots.

Dimensions reference: Microchip C04-070, page 42 (PDF page 47). Drill/pad diameters retain the configurable DIP defaults.

GitHub CI on f7a59ac: 570 tests pass / 0 fail; build, format-check and Format code also pass. Test run.

Additional local validation on Windows / Bun 1.4.2:

• Focused SPDIP + DIP tests: 17 pass, including exact pin coordinates/order, aliases, custom drill sizes and global modifiers. SVG preview visually inspected.
• bun run --bun build: ESM and declaration build pass.
• Full bun test: 566 pass / 4 fail. SMF and both SOD523 snapshot failures also reproduce with the original source at d0d2ee1; MELF parity timed out in the full run and passed in the focused baseline run.
• Full-repository tsc --noEmit reports errors in other source/tests; it is not claimed as passing. No errors reported for the added SPDIP files.

The issue mentions a possible $10 bounty. Please confirm eligibility if this contribution is accepted.

[ikoomm]

Resolved the merge conflict with current main while retaining the SPDIP alias and the newly added standard diode aliases. All 24 focused package/regression tests pass locally, and the build, test and format checks pass on commit 198e5b5. Ready for review.