feat: convert postgresclient module to independent sal-postgresclient package

- Move src/postgresclient/ to postgresclient/ package structure
- Add comprehensive test suite (28 tests) with real PostgreSQL operations
- Maintain Rhai integration with all 10 wrapper functions
- Update workspace configuration and dependencies
- Add complete documentation with usage examples
- Remove old module and update all references
- Ensure zero regressions in existing functionality

Closes: postgresclient monorepo conversion

postgresclient/tests/rhai/test_simple.rhai

@@ -0,0 +1,22 @@
+// Simple test script to verify that the Rhai engine is working
+
+print("Hello, world!");
+
+// Try to access the PostgreSQL installer functions
+print("\nTrying to access PostgreSQL installer functions...");
+
+// Try to call the pg_install function
+try {
+    let result = pg_install(
+        "postgres-test",
+        "15",
+        5433,
+        "testuser",
+        "testpassword"
+    );
+    print("pg_install result: " + result);
+} catch(e) {
+    print("Error calling pg_install: " + e);
+}
+
+print("\nTest completed!");