Add synthetic frame for lxml schema init

Creating schema in lxml can be a performance issue if we always recreate
a schema instead of reusing it.

Unfortunately this code is cython and does not appear in the flame
graph, this change searches for `etree.XMLSchema(` in the source code
line to add a synthetic frame for it to appear in the graph.

Tested with a local script.

Author: PapaPedro

codeguru_profiler_agent/sampling_utils.py

@@ -10,6 +10,7 @@
 TRUNCATED_FRAME = Frame(name="<Truncated>")
 
 TIME_SLEEP_FRAME = Frame(name="<Sleep>")
+LXML_SCHEMA_FRAME = Frame(name="lxml.etree:XMLSchema:__init__")
 
 
 def get_stacks(threads_to_sample, excluded_threads, max_depth):
@@ -69,14 +70,16 @@ def _extract_stack(stack, max_depth):
         )
     if len(stack) < max_depth:
         last_frame, last_frame_line_no = stack[-1]
-        _maybe_append_time_sleep(result, last_frame, last_frame_line_no)
+        _maybe_append_synthetic_frame(result, last_frame, last_frame_line_no)
     return result
 
 
-def _maybe_append_time_sleep(result, frame, line_no):
+def _maybe_append_synthetic_frame(result, frame, line_no):
     line = linecache.getline(frame.f_code.co_filename, line_no).strip()
     if "sleep(" in line:
         result.append(TIME_SLEEP_FRAME)
+    elif "etree.XMLSchema(" in line:
+        result.append(LXML_SCHEMA_FRAME)
 
 
 def _extract_frames(end_frame, max_depth):