perf: defer tracker initialization and slim import path (1/4) (#1251)

* perf: defer tracker initialization and slim import path

Lazy-load reference data, output handlers, hardware probing, and the
emissions engine so tracker construction stays fast when work is deferred.

Co-authored-by: Cursor <cursoragent@cursor.com>

* test: initialize hardware before cpu_load detection assertion

Deferred hardware setup in PR 1 requires _ensure_hardware_ready() in tests
that inspect tracker._hardware before start().

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix: restore pandas DataFrame type hints in input.py

Use TYPE_CHECKING import for pd so lazy loading stays fast while keeping
return type annotations on get_cloud_emissions_data and get_cpu_power_data.

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: davidberenstein1957

codecarbon/__init__.py

@@ -8,7 +8,7 @@
     OfflineEmissionsTracker,
     track_emissions,
 )
-from .output import OutputMethod
+from .output_methods.base_output import OutputMethod
 
 __all__ = [
     "EmissionsTracker",

codecarbon/core/api_client.py

@@ -10,7 +10,6 @@
 import json
 from datetime import timedelta, tzinfo
 
-import arrow
 import requests
 
 from codecarbon.core.schemas import (
@@ -22,12 +21,11 @@
 )
 from codecarbon.external.logger import logger
 
-# from codecarbon.output import EmissionsData
-
 
 def get_datetime_with_timezone():
-    timestamp = str(arrow.now().isoformat())
-    return timestamp
+    import arrow
+
+    return str(arrow.now().isoformat())
 
 
 class ApiClient:  # (AsyncClient)

codecarbon/core/util.py

@@ -8,7 +8,6 @@
 from pathlib import Path
 from typing import Optional, Union
 
-import cpuinfo
 import psutil
 
 from codecarbon.external.logger import logger
@@ -76,6 +75,8 @@ def backup(file_path: Union[str, Path], ext: Optional[str] = ".bak") -> None:
 
 @lru_cache(maxsize=1)
 def detect_cpu_model() -> Optional[str]:
+    import cpuinfo
+
     cpu_info = cpuinfo.get_cpu_info()
     if cpu_info:
         cpu_model_detected = cpu_info.get("brand_raw", "")