fix(feature-processor): Add clarifying comment for legacy env var and explicit cryptography dep

Add comment explaining REMOTE_FUNCTION_SECRET_KEY is a legacy misnomer —
the value is an ECDSA public key for signature verification, not a secret.
Add cryptography>=46.0.0 as explicit dependency in sagemaker-mlops.

---
X-AI-Prompt: resolve CR comment about misleading REMOTE_FUNCTION_SECRET_KEY naming and missing cryptography dependency
X-AI-Tool: kiro

Author: BassemHalim

sagemaker-mlops/pyproject.toml

@@ -26,6 +26,7 @@ dependencies = [
     "sagemaker-core>=2.10.1",
     "sagemaker-train>=1.10.1",
     "sagemaker-serve>=1.10.1",
+    "cryptography>=46.0.0",
     "boto3>=1.42.2,<2.0",
     "botocore>=1.42.2,<2.0",
     "pyiceberg[glue]>=0.8.0",

sagemaker-mlops/src/sagemaker/mlops/feature_store/feature_processor/feature_scheduler.py

@@ -871,6 +871,8 @@ def _prepare_model_trainer_from_remote_decorator_config(
     # Build environment dict from remote_decorator_config
     environment = dict(remote_decorator_config.environment_variables or {})
     if public_key_pem:
+        # Legacy env var name — value is the ECDSA public key used by the container
+        # (invoke_function.py) for asymmetric signature verification, not a secret.
         environment["REMOTE_FUNCTION_SECRET_KEY"] = public_key_pem
 
     # Build command from container entry point and arguments