Fix telemetry singleton pattern to respect dynamic environment variables (#2946)

* Fix telemetry singleton pattern to respect dynamic environment variables

- Modified Telemetry.__init__ to prevent re-initialization with _initialized flag
- Updated _safe_telemetry_operation to check _is_telemetry_disabled() dynamically
- Added comprehensive tests for environment variables set after singleton creation
- Fixed singleton contamination in existing tests by adding proper reset
- Resolves issue #2945 where CREWAI_DISABLE_TELEMETRY=true was ignored when set after import

Co-Authored-By: João <joao@crewai.com>

* Implement code review improvements

- Move _initialized flag to __new__ method for better encapsulation
- Add type hints to _safe_telemetry_operation method
- Consolidate telemetry execution checks into _should_execute_telemetry helper
- Add pytest fixtures to reduce test setup redundancy
- Enhanced documentation for singleton behavior

Co-Authored-By: João <joao@crewai.com>

* Fix mypy type-checker errors

- Add explicit bool type annotation to _initialized field
- Fix return value in task_started method to not return _safe_telemetry_operation result
- Simplify initialization logic to set _initialized once in __init__

Co-Authored-By: João <joao@crewai.com>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: João <joao@crewai.com>
Co-authored-by: Lorenze Jay <63378463+lorenzejay@users.noreply.github.com>

src/crewai/telemetry/telemetry.py

@@ -8,7 +8,7 @@ import platform
 import warnings
 from contextlib import contextmanager
 from importlib.metadata import version
-from typing import TYPE_CHECKING, Any, Optional
+from typing import TYPE_CHECKING, Any, Callable, Optional
 import threading
 
 from opentelemetry import trace
@@ -73,11 +73,16 @@ class Telemetry:
             with cls._lock:
                 if cls._instance is None:
                     cls._instance = super(Telemetry, cls).__new__(cls)
+                    cls._instance._initialized = False
         return cls._instance
 
     def __init__(self) -> None:
+        if hasattr(self, '_initialized') and self._initialized:
+            return
+        
         self.ready: bool = False
         self.trace_set: bool = False
+        self._initialized: bool = True
 
         if self._is_telemetry_disabled():
             return
@@ -113,6 +118,10 @@ class Telemetry:
             or os.getenv("CREWAI_DISABLE_TELEMETRY", "false").lower() == "true"
         )
 
+    def _should_execute_telemetry(self) -> bool:
+        """Check if telemetry operations should be executed."""
+        return self.ready and not self._is_telemetry_disabled()
+
     def set_tracer(self):
         if self.ready and not self.trace_set:
             try:
@@ -123,8 +132,9 @@ class Telemetry:
                 self.ready = False
                 self.trace_set = False
 
-    def _safe_telemetry_operation(self, operation):
-        if not self.ready:
+    def _safe_telemetry_operation(self, operation: Callable[[], None]) -> None:
+        """Execute telemetry operation safely, checking both readiness and environment variables."""
+        if not self._should_execute_telemetry():
             return
         try:
             operation()
@@ -423,7 +433,8 @@ class Telemetry:
 
             return span
 
-        return self._safe_telemetry_operation(operation)
+        self._safe_telemetry_operation(operation)
+        return None
 
     def task_ended(self, span: Span, task: Task, crew: Crew):
         """Records the completion of a task execution in a crew.
@@ -773,7 +784,8 @@ class Telemetry:
             return span
 
         if crew.share_crew:
-            return self._safe_telemetry_operation(operation)
+            self._safe_telemetry_operation(operation)
+            return operation()
         return None
 
     def end_crew(self, crew, final_string_output):