schema support for declarative column definitions

[0.5.11] - 2026-02-02

Added

• Added optional schema class support for declarative column definitions using Python type annotations.
• Added default_record() method to create new records initialized from schema defaults.
• Added text to README.md to explain the new schema approach.
• Added decorator approach to schemaclass and placed in a separate file schemaclass.py with schemaclass_README.md in /lib
• Added method .attach_schema(self, schema: type) to allow schema to be attached after reading the file.

Changed

• daf.keys() now has optional parameter 'silent_error' which defaults to True.
  • If True and there is no keyfield set, do not produce KeysDisabledError and instead return []
  • If False, raise KeysDisabledError
• added compatibility for astype_la() to use type values like int,str,float,bool as well as int,str, etc.
• apply_dtypes() now enforces exact match by default
  • Use silent_error=True to allow mismatches.