fix(linux): reduce AppImage boot time from ~50s to near-instant

Change compression from "maximum" to "normal" for electron-builder.

The "maximum" compression setting causes gzip/xz compression in the
squashfs filesystem, which has extremely poor random access performance
(~35 MB/s). This results in 50+ second boot times on Linux AppImage
releases due to FUSE overhead during Electron's many small file reads
at startup.

With "normal" compression, the AppImage uses faster decompression
algorithms, dramatically improving startup time while only marginally
increasing package size.

Refs: electron-userland/electron-builder#6317
Refs: electron-userland/electron-builder#7483

electron-builder.json5

@@ -6,7 +6,7 @@
   "productName": "Openscreen",
   "npmRebuild": true,
   "buildDependenciesFromSource": true,
-  "compression": "maximum",
+  "compression": "normal",
   "directories": {
     "output": "release/${version}"
   },