[Python Observability] Make sure call_tracers are deleted (#37247)

Make sure call_tracers are deleted as long as c_call is unrefed.

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Closes #37247

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/37247 from XuanWang-Amos:fixHangingCallTracers b22a45cca9
PiperOrigin-RevId: 654865870

src/python/grpcio/grpc/_cython/_cygrpc/channel.pxd.pxi

@@ -31,6 +31,7 @@ cdef class _CallState:
   cdef void maybe_save_registered_method(self, bytes method_name) except *
   cdef void maybe_set_client_call_tracer_on_call(self, bytes method_name, bytes target) except *
   cdef void maybe_delete_call_tracer(self) except *
+  cdef void delete_call(self) except *
 
 
 cdef class _ChannelState:

src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi

@@ -72,6 +72,12 @@ cdef class _CallState:
   def __cinit__(self):
     self.due = set()
 
+  cdef void delete_call(self) except *:
+    with nogil:
+      grpc_call_unref(self.c_call)
+    self.c_call = NULL
+    self.maybe_delete_call_tracer()
+
   cdef void maybe_delete_call_tracer(self) except *:
     if not self.call_tracer_capsule:
       return
@@ -291,9 +297,7 @@ cdef void _call(
         grpc_call_credentials_release(c_call_credentials)
         if c_call_error != GRPC_CALL_OK:
           #TODO(xuanwn): Expand the scope of nogil
-          with nogil:
-            grpc_call_unref(call_state.c_call)
-          call_state.c_call = NULL
+          call_state.delete_call()
           _raise_call_error_no_metadata(c_call_error)
       started_tags = set()
       for operations, user_tag in operationses_and_user_tags:
@@ -303,9 +307,7 @@ cdef void _call(
         else:
           grpc_call_cancel(call_state.c_call, NULL)
           #TODO(xuanwn): Expand the scope of nogil
-          with nogil:
-            grpc_call_unref(call_state.c_call)
-          call_state.c_call = NULL
+          call_state.delete_call()
           _raise_call_error(c_call_error, metadata)
       else:
         call_state.due.update(started_tags)
@@ -319,10 +321,7 @@ cdef void _process_integrated_call_tag(
   cdef _CallState call_state = state.integrated_call_states.pop(tag)
   call_state.due.remove(tag)
   if not call_state.due:
-    with nogil:
-      grpc_call_unref(call_state.c_call)
-    call_state.c_call = NULL
-    call_state.maybe_delete_call_tracer()
+    call_state.delete_call()
 
 cdef class IntegratedCall:
 
@@ -362,10 +361,7 @@ cdef object _process_segregated_call_tag(
   call_state.due.remove(tag)
   if not call_state.due:
     #TODO(xuanwn): Expand the scope of nogil
-    with nogil:
-      grpc_call_unref(call_state.c_call)
-    call_state.c_call = NULL
-    call_state.maybe_delete_call_tracer()
+    call_state.delete_call()
     state.segregated_call_states.remove(call_state)
     _destroy_c_completion_queue(c_completion_queue)
     return True
@@ -392,9 +388,7 @@ cdef class SegregatedCall:
         self._channel_state, self._call_state, self._c_completion_queue, tag)
     def on_failure():
       self._call_state.due.clear()
-      with nogil:
-        grpc_call_unref(self._call_state.c_call)
-      self._call_state.c_call = NULL
+      self._call_state.delete_call()
       self._channel_state.segregated_call_states.remove(self._call_state)
       _destroy_c_completion_queue(self._c_completion_queue)
     return _next_call_event(