feat: Add workspace-level linting rules and cargo-audit configuration

- Add cargo-audit metadata section with placeholder for ignored advisories
- Forbid unsafe_code at workspace level
- Enable all and pedantic clippy warnings
- Deny unwrap_used, expect_used, and panic to enforce error handling
- Add thiserror dependency to charging-engine for improved error handling

Cargo.toml

@@ -12,6 +12,20 @@ edition = "2021"
 rust-version = "1.94"
 license = "MIT"
 
+[workspace.metadata.cargo-audit]
+# Ignore advisories that are not relevant to this project
+# advisories = []
+
+[workspace.lints.rust]
+unsafe_code = "forbid"
+
+[workspace.lints.clippy]
+all = "warn"
+pedantic = "warn"
+unwrap_used = "deny"
+expect_used = "deny"
+panic = "deny"
+
 [workspace.dependencies]
 # Async runtime
 tokio = { version = "1.52.1", features = ["full"] }

apps/charging-engine/Cargo.toml

@@ -25,6 +25,7 @@ serde_json = { workspace = true }
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
 anyhow = { workspace = true }
+thiserror = "2.0.18"
 dotenv = { workspace = true }
 uuid = { workspace = true }
 jsonwebtoken = "10.3.0"