Demo Ready

• Cleanup a lot of go files to be production ready.

One base, many overlays

Initial release of blockdev: an in-memory copy-on-write block device in Go for sandbox snapshot/resume.

Many sandboxes share one immutable base in RAM; each captures its writes in a per-instance overlay; Serialize emits only the changed blocks.

• Public API: New, ReadAt(io.ReaderAt), WriteAt (io.WriterAt), Serialize, Deserialize, plus WithName / WithObserver
  for instrumentation. Drops in wherever io.ReaderAt/io.WriterAt would fit.

• Wire format is [8B BE block#][4096B data] per changed block, sorted ascending, locked by a golden-bytes test: any future change requires a major version bump. Stdlib-only, Go 1.22+.

• 14 benchmarks publish a continuously-updated chart at https://codingminions.github.io/blockdev/dev/bench/;