refactor: simplify settings to pure pydantic without backward compat

- Remove ConfigWrapper class and backward compatibility layer
- Use direct pydantic BaseSettings with typed nested models
- Change context manager from config(...) to config.override(...)
- Add validate_assignment=True for runtime type checking
- Improve store spec validation with clear error messages
- Update all tests to use new API
- Preserve dict-style access via __getitem__/__setitem__ for convenience

Author: claude

src/datajoint/jobs.py

@@ -76,7 +76,7 @@ def reserve(self, table_name, key):
             user=self._user,
         )
         try:
-            with config(enable_python_native_blobs=True):
+            with config.override(enable_python_native_blobs=True):
                 self.insert1(job, ignore_extra_fields=True)
         except DuplicateError:
             return False
@@ -107,7 +107,7 @@ def ignore(self, table_name, key):
             user=self._user,
         )
         try:
-            with config(enable_python_native_blobs=True):
+            with config.override(enable_python_native_blobs=True):
                 self.insert1(job, ignore_extra_fields=True)
         except DuplicateError:
             return False
@@ -135,7 +135,7 @@ def error(self, table_name, key, error_message, error_stack=None):
         """
         if len(error_message) > ERROR_MESSAGE_LENGTH:
             error_message = error_message[: ERROR_MESSAGE_LENGTH - len(TRUNCATION_APPENDIX)] + TRUNCATION_APPENDIX
-        with config(enable_python_native_blobs=True):
+        with config.override(enable_python_native_blobs=True):
             self.insert1(
                 dict(
                     table_name=table_name,