fix(nix): share Gradle home so worktree daemons stop piling up (#1339)

gradle.properties

@@ -7,6 +7,8 @@
 # Specifies the JVM arguments used for the daemon process.
 # The setting is particularly useful for tweaking memory settings.
 org.gradle.jvmargs=-Xmx2048m -Dfile.encoding=UTF-8
+# Stop idle daemons after 20 min (default 3 h) so finished builds release their RAM.
+org.gradle.daemon.idletimeout=1200000
 # Enables Gradle Build Cache.
 # See https://docs.gradle.org/current/userguide/build_cache.html
 org.gradle.caching=true