feat: add buffer lookup and location results update to services

## Changes
- Add findInBuffer() to BufferService for looking up checks still in the write buffer
- Add updateLocationResults() to IChecksRepository interface and MongoChecksRepository
- Update GlobalpingService to return GlobalpingCheckResult[] instead of MonitorStatusResponse[]

## Benefits
Non-destructive service additions that prepare the backfill pipeline.
Existing check-writing and Globalping flows are unchanged.

server/src/service/infrastructure/bufferService.ts

@@ -5,6 +5,7 @@ const SERVICE_NAME = "BufferService";
 export interface IBufferService {
 	addToBuffer(check: Check): void;
 	removeCheckFromBuffer(check: Check): boolean;
+	findInBuffer(checkId: string): Check | undefined;
 	scheduleNextFlush(): void;
 	flushBuffer(): Promise<void>;
 }
@@ -49,6 +50,10 @@ class BufferService implements IBufferService {
 		}
 	}
 
+	findInBuffer(checkId: string): Check | undefined {
+		return this.buffer.find((c: Check) => c.id?.toString() === checkId);
+	}
+
 	removeCheckFromBuffer(checkToRemove: Check) {
 		try {
 			if (!checkToRemove) {