wendelin_telecom_base: Update data chunk size limits in KPI calculation process

- Reduce maximum data chunk size for new data
- Add a maximum data chunk size for the previous data to bound computing time

bt5/wendelin_telecom_base/PathTemplateItem/portal_callables/DataAnalysisLine_calculateOrsEnbKpi.py

 import json
 import numpy as np
 
-MAX_CHUNK_SIZE = 10000000 # bytes
+MAX_PREV_CHUNK_SIZE = 1024 * 1024 # bytes
+MAX_NEW_CHUNK_SIZE = 1024 * 1024 # bytes
 HISTORY_LINE_COUNT = 64
 T_PERIOD = 30 # seconds
 QCI_COUNT = 256
@@ -9,8 +10,8 @@ QCI_COUNT = 256
 in_data_stream = in_stream['Data Stream']
 progress_indicator = in_stream['Progress Indicator']
 offset_index = progress_indicator.getIntOffsetIndex()
-start = 0
-end = min(in_data_stream.getSize(), offset_index + MAX_CHUNK_SIZE)
+start = max(0, offset_index - MAX_PREV_CHUNK_SIZE)
+end = min(in_data_stream.getSize(), offset_index + MAX_NEW_CHUNK_SIZE)
 
 # No new data to process
 if offset_index >= end:
@@ -22,7 +23,11 @@ new_log_data = ''.join(in_data_stream.readChunkList(offset_index, end))
 previous_log_data_line_list = previous_log_data.splitlines()
 new_log_data_line_list = new_log_data.splitlines()
 
-# Last new log line may not be valid JSON due to MAX_CHUNK_SIZE:
+# First previous log line may not be valid JSON due to MAX_PREV_CHUNK_SIZE:
+# Simply discard it
+previous_log_data_line_list = previous_log_data_line_list[1:]
+
+# Last new log line may not be valid JSON due to MAX_NEW_CHUNK_SIZE:
 # In that case, leave it to the next KPI calculation
 last_new_log_data_line = new_log_data_line_list[-1]
 try: