feat: add remaining() method to check requests left for an IP (JhaSourav07#1638)

## Description

Adds a `remaining(ip)` method to `RateLimiter` that returns how many
requests an IP has left in the current window without consuming one.
Useful for setting `X-RateLimit-Remaining` response headers without
side effects.

Fixes JhaSourav07#1634 


## Pillar
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview
N/A — internal rate limiting logic, no visual output.

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- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally.
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resolved all errors.
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- [x] I have updated `README.md` if I added a new theme or URL
parameter.
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standard.
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Author: JhaSourav07

lib/rate-limit.ts

@@ -107,6 +107,24 @@ export class RateLimiter {
   async reset(ip: string): Promise<void> {
     await this.cache.delete(ip);
   }
+  /**
+   * Returns the number of remaining requests allowed for a given IP
+   * in the current window.
+   *
+   * Does not consume a request — use `check()` for that.
+   *
+   * @param ip - The IP address to check.
+   * @returns Promise resolving to the number of remaining requests,
+   *          or the full limit if the IP has no recorded requests.
+   *
+   * @example
+   * const left = await rateLimiter.remaining("192.168.1.1");
+   * console.log(`You have ${left} requests left.`);
+   */
+  async remaining(ip: string): Promise<number> {
+    const current = (await this.cache.get(ip)) ?? 0;
+    return Math.max(0, this.limit - current);
+  }
 
   allow(ip: string): void {
     this.allowlist.add(ip);