feat: Add lazy default package resolution.

[dylan-sutton-chavez]

No description provided.

[dylan-sutton-chavez]

• Re-point the test at the CDN once the new wasm ships. The route currently serves a local compiler_lib.wasm because the published one is missing extract_imports. Temporary scaffold, delete the branch when the CDN catches up.

I reverted to the main branch in the last commit before this pull request; I'm still using a CDN for all pushes. I'm going to temporarily decouple the necessary tests.

• Version-gate the ABI bump. New runtime + old CDN wasm throws extract_imports missing on every run. Either expose an abi_version export and check it at load, or fall back to the old quoted-only scanner so old wasm degrades instead of breaking.

Doesn't matter, just std and host packages.

• pendingBare drops importers. It's Map<name, dir>, so a second importer of the same unresolved name overwrites
  the first and relative targets resolve against the wrong dir. Make it Map<name, dir[]>.

Fixed using Map<name, dir[]>

• No test for defaults: false. We prove defaults work and are lazy, but nothing proves the opt-out actually opts out. Add a run with defaults: false that imports json and expects a resolution error.

n/A

• engine.js imports DEFAULT_IMPORTS directly. The doc says defaults are a browser-runtime convenience, not a worker concern, but the worker reaches into defaults.js. Pass them in via load opts so the engine stays embedder-neutral.

Merging DEFAULT_IMPORTS in the index.js side to decouple the compiler from the runtime