Remove private parser functions from config module public interface

Removed _parse_config_file and _parse_config from chipflow_lib.config
imports. These are internal/private functions (indicated by underscore
prefix) and should not be accessible via the config module's public
interface.

Updated:
- chipflow_lib/config/__init__.py: Removed imports of private functions
- chipflow_lib/__init__.py: Import _parse_config directly from config.parser
- tests/test_init.py: Import _parse_config_file from config.parser submodule

These functions remain accessible internally but are no longer exposed
as part of the config module's public API.

Author: robtaylor

chipflow_lib/__init__.py

@@ -31,7 +31,7 @@
 
 def _parse_config() -> 'Config':
     """Parse the chipflow.toml configuration file."""
-    from .config import _parse_config as config_parse
+    from .config.parser import _parse_config as config_parse
     return config_parse()
 
 

chipflow_lib/config/__init__.py

@@ -24,8 +24,6 @@
 from .parser import (
     get_dir_models,
     get_dir_software,
-    _parse_config_file,
-    _parse_config,
 )
 
 __all__ = [

tests/test_init.py

@@ -13,7 +13,7 @@
     _ensure_chipflow_root,
     _parse_config
 )
-from chipflow_lib.config import _parse_config_file
+from chipflow_lib.config.parser import _parse_config_file
 from chipflow_lib.config_models import Config, ChipFlowConfig
 # Process is not part of the public API, so we won't test it here