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

Cargo.toml

@@ -11,7 +11,7 @@ categories = ["os", "filesystem", "api-bindings"]
 readme = "README.md"
 
 [workspace]
-members = [".", "vault", "git", "redisclient", "mycelium", "text", "os", "net", "zinit_client", "process", "virt"]
+members = [".", "vault", "git", "redisclient", "mycelium", "text", "os", "net", "zinit_client", "process", "virt", "postgresclient"]
 
 [dependencies]
 hex = "0.4"
@@ -68,6 +68,7 @@ sal-net = { path = "net" }
 sal-zinit-client = { path = "zinit_client" }
 sal-process = { path = "process" }
 sal-virt = { path = "virt" }
+sal-postgresclient = { path = "postgresclient" }
 
 # Optional features for specific OS functionality
 [target.'cfg(unix)'.dependencies]