fix(tracemetrics): Bump metric buffer to 1k

We've been noticing some discards from clients for likely buffer reason (primarily on python, though fixing it on both). Metrics were initially set to 100 to match logs but the size limit for a metric is ~1000x less (~1-2kb at the moment) so the memory pressure should be fine.

packages/core/src/metrics/internal.ts

@@ -12,7 +12,7 @@ import { timestampInSeconds } from '../utils/time';
 import { _getTraceInfoFromScope } from '../utils/trace-info';
 import { createMetricEnvelope } from './envelope';
 
-const MAX_METRIC_BUFFER_SIZE = 100;
+const MAX_METRIC_BUFFER_SIZE = 1000;
 
 /**
  * Converts a metric attribute to a serialized metric attribute.