Update tests with three packages: just-bash, zen-test, zen-bash

- packages/just-bash: Succinct basic fs operation tests for just-bash
- packages/zen-test: Basic file operations with @zenfs/core (memory backend)
- packages/zen-bash: Demonstrates combining just-bash with @zenfs/core

All tests pass (37 total tests across 3 packages)

Author: pyramation

packages/just-bash/.eslintrc.json

@@ -0,0 +1,3 @@
+{
+  "extends": ["../../.eslintrc.json"]
+}