feat(plugin-crop): add autocropRect helper

[Aniketiitk21]

Summary

• add image.autocropRect(options) so callers can inspect the exact { x, y, w, h } rectangle that autocrop() would apply
• refactor autocrop() to reuse the same rectangle calculation logic, keeping the mutating crop behavior aligned with the new helper
• add plugin-level and public-entrypoint tests so the helper is validated both inside @jimp/plugin-crop and through jimp
• replace @jimp/plugin-print's shell-specific cp -r build step with a small Node copy script so the wider Jimp build works on Windows too

Why

Today autocrop() can remove borders, but it does not expose the crop rectangle it found. That makes atlas packing, layout alignment, and preflight inspection awkward because consumers have to either rescan the image or mutate it first just to discover the offsets.

This adds a small read-only API that returns the same rectangle autocrop() would use, which means callers can inspect it, store it, or pass it directly into crop().

While validating the change on Windows, the wider jimp... build surfaced a separate portability problem in @jimp/plugin-print: its build script still depended on cp -r. Fixing that keeps the workspace build path consistent across platforms and removes a real validation blocker.

Implementation

• add autocropRect(options) to @jimp/plugin-crop
• factor the existing autocrop side-scanning logic into a shared internal helper
• return the full image bounds when the current options would result in no crop
• keep autocrop() behavior unchanged by making it consume the same computed rectangle
• document the helper in the crop plugin README
• update @jimp/plugin-print to copy its bundled fonts with node:fs/promises.cp() instead of a shell-only cp -r

Validation

• pnpm exec turbo run build --filter=@jimp/plugin-crop...
• pnpm exec turbo run test --filter=@jimp/plugin-crop -- --run
• pnpm --filter @jimp/plugin-crop lint
• pnpm --filter @jimp/plugin-crop build
• pnpm --filter jimp test -- --run src/jimp.test.ts
• pnpm --filter @jimp/plugin-print build
• pnpm exec turbo run build --filter=jimp...

Closes #801