fix(metrics): address PR #11 code review feedback

Major improvements to prometheus-metrics.ts:
- Use custom registry instead of global promClient.register (isolation)
- Remove duplicate localValues - prom-client is now single source of truth
- Fix reset(labels) to respect labels param using remove() instead of reset()
- Migrate Summary class to use prom-client internally
- getMetricsOutput() now uses customRegistry for proper isolation

Fix misleading comments in retry-utils.ts:
- Change "exponential backoff" to "custom progressive backoff"
- Fix comment claiming constants are "from Defaults" (now local)

Breaking changes to getValues()/get() - now async as they query prom-client

src/Utils/retry-utils.ts

@@ -18,8 +18,8 @@ import { metrics } from './prometheus-metrics.js'
 import type { CircuitBreaker } from './circuit-breaker.js'
 
 /**
- * Retry configuration with exponential backoff
- * Delays in milliseconds: 1s, 2s, 5s, 10s, 20s
+ * Retry configuration with custom progressive backoff
+ * Fixed delay steps in milliseconds: 1s → 2s → 5s → 10s → 20s
  * Defined locally to avoid circular dependency with Defaults
  */
 const RETRY_BACKOFF_DELAYS = [1000, 2000, 5000, 10000, 20000]
@@ -669,7 +669,7 @@ export const retryConfigs = {
 
 /**
  * Get retry delay with jitter applied
- * Uses RETRY_BACKOFF_DELAYS and RETRY_JITTER_FACTOR from Defaults
+ * Uses RETRY_BACKOFF_DELAYS and RETRY_JITTER_FACTOR defined locally
  *
  * @param attempt - Current attempt number (1-based)
  * @returns Delay in ms with jitter applied