chore: Get build working on linux again, hopefully w/o disrupting windows (#2)

Just puts the package.json contents into a file and copies it in place.

Reviewed-on: #2
Co-authored-by: Glen Whitney <glen@studioinfinity.org>
Co-committed-by: Glen Whitney <glen@studioinfinity.org>

etc/package.json

@@ -0,0 +1 @@
+{"type": "module"}

package.json5

@@ -3,7 +3,7 @@
    version: '0.0.1',
    description: 'Another prototype for a math core',
    scripts: {
-      build: 'tsc && echo {"type": "module"} > build/package.json',
+      build: 'tsc && cp etc/package.json build/',
       go: 'pnpm build && pnpm start',
       prepare: 'ts-patch install -s',
       start: 'node --experimental-loader tsc-module-loader build',