DRAFT: Combine spark-worker-rs and spark-rs into one

[mrxz]

Related to #321 and builds upon: #322

This PR combines the spark-worker-rs and spark-rs projects into one, reducing bloat of shared code/logic that would otherwise end up in both .wasm files. To avoid the combined .wasm file from being embedded multiple times into the bundle, the WASM module is now passed along to the workers, removing the embedded copy in the embedded worker code.

The flow is as follows:

• wasm.ts automatically kicks off the WASM compiling
• wasm.ts automatically kicks off the initialization of the spark-rs project for the main thread
• The SplatMesh no longer statically initializes spark-rs, but instead checks the initialization status through wasm.ts
• The SplatPager no longer initializes spark-rs, but instead awaits initialization through wasm.ts
• The workers now await an init-wasm message with the WASM module

This has a couple of benefits, namely that the wasm blob is only embedded once. The webpack/Next.js workaround is no longer needed. And the WASM module is compiled only once across main thread and workers.

With one less rust project, the build:wasm script also takes less time. :-)