refactor: Simplify rate limiter to use default configuration in charging-engine

- Remove unused imports: governor clock/state/Quota, std::num::NonZeroU32, std::sync::Arc, and SmartIpKeyExtractor
- Change create_rate_limiter return type from explicit generic parameters to simple GovernorLayer
- Replace custom rate limit configuration (RATE_LIMIT_RPS, RATE_LIMIT_BURST environment variables) with GovernorConfig::default()
- Remove quota builder logic and pass config directly to GovernorLayer::new()

apps/charging-engine/src/rate_limit.rs

@@ -2,39 +2,15 @@ use axum::{
     http::StatusCode,
     response::{IntoResponse, Response},
 };
-use governor::{
-    clock::DefaultClock,
-    state::InMemoryState,
-    Quota,
-};
-use std::num::NonZeroU32;
-use std::sync::Arc;
 use tower_governor::{
     governor::GovernorConfig,
-    key_extractor::SmartIpKeyExtractor,
     GovernorLayer,
 };
 
-pub fn create_rate_limiter() -> GovernorLayer<SmartIpKeyExtractor, InMemoryState, DefaultClock> {
-    let requests_per_second: u32 = std::env::var("RATE_LIMIT_RPS")
-        .ok()
-        .and_then(|s| s.parse().ok())
-        .unwrap_or(10);
-    let burst_size: u32 = std::env::var("RATE_LIMIT_BURST")
-        .ok()
-        .and_then(|s| s.parse().ok())
-        .unwrap_or(20);
+pub fn create_rate_limiter() -> GovernorLayer {
+    let governor_conf = GovernorConfig::default();
 
-    let quota = Quota::per_second(NonZeroU32::new(requests_per_second).unwrap())
-        .allow_burst(NonZeroU32::new(burst_size).unwrap());
-
-    let config = GovernorConfig::builder()
-        .per_second(quota)
-        .burst_size(burst_size)
-        .finish()
-        .unwrap();
-
-    GovernorLayer::new(&config)
+    GovernorLayer::new(governor_conf)
 }
 
 pub struct RateLimitResponse;