fix: load classic blob worker main script directly (#34592)

## Summary

- Load classic worker main scripts by their resolved URL instead of
importing `#` from the synthetic worker eval script.
- Add regression coverage for blob URL classic workers: normal Deno
rejects them immediately, while the testing-enabled classic path can
postMessage back to the parent.

## Tests

- `CARGO_INCREMENTAL=0 cargo test -p specs_tests --test specs --
classic_worker_blob_url`

Closes denoland/orchid#337

Co-authored-by: divybot <divybot@users.noreply.github.com>
Co-authored-by: Divy Srivastava <me@littledivy.com>