fix: Fix HTJ2K decoder leak

Commit 85fd193 changed decodeHTJ2K.js
to allocate a new HTJ2KDecoder with each call to decodeAsync. The old
decoders somehow stay alive, and are not cleaned from the WASM memory.
Each new HTJ2KDecoder allocates in turns buffers for the encoded and
decoded pixel data while decoding.

The change to allocate a new decoder per frame argued that reusing the
old decoder is "much slower", but I could not reproduce any slowdowns
either in the browser or on Node. This commit therefore reverts the
change, so that each call to decodeAsync reuses the same decoder
instance.

packages/dicomImageLoader/src/shared/decoders/decodeHTJ2K.ts

@@ -57,8 +57,7 @@ export function initialize(decodeConfig?: LoaderDecodeOptions): Promise<void> {
 // https://github.com/chafey/openjpegjs/blob/master/test/browser/index.html
 async function decodeAsync(compressedImageFrame: ByteArray, imageInfo) {
   await initialize();
-  // const decoder = local.decoder; // This is much slower for some reason
-  const decoder = new local.codec.HTJ2KDecoder();
+  const decoder = local.decoder;
 
   // get pointer to the source/encoded bit stream buffer in WASM memory
   // that can hold the encoded bitstream