Add Apache 2.0 license headers and related scripts to the repository

Summary

• Adds the Copyright (c) 2023-2026 CLOUDRISK Limited and FT Advisory LLC / SPDX-License-Identifier: Apache-2.0 header to every .py, .yml, .sh, and .toml file in the repository, and puts tooling in place to keep it enforced going forward.
• Fixes a pydantic 2.12 compatibility break in BaseDataClass._serialize_refs that caused all model serialization to fail with a PydanticSerializationError.

What changed

License headers

• Added src/license/header.txt (the header template) and src/license/apply_headers.sh (applies headers across all directories and root files in one command)
• Applied the header to all tracked source and config files (.py, .yml, .sh, .toml)
• Added .pre-commit-config.yaml with two licenseheaders hooks (managed by pre-commit, no manual venv setup needed) — triggered on commit for all covered file types
• Added .github/workflows/check-license-headers.yml — CI backstop that fails the build if any file is missing a header on push/PR to main or develop
• Updated dev_clean_setup.sh to run pre-commit install automatically, so hooks are active for any developer who follows the standard setup
• Updated README.md with the header format and the fix command

pydantic 2.12 compatibility fix

BaseDataClass._serialize_refs is decorated with @model_serializer(mode='wrap'). The wrap handler callable (SerializerFunctionWrapHandler) only accepts the value to serialize — SerializationInfo is passed to the outer function but must not be forwarded to the handler. In pydantic ≤ 2.11 the extra argument was silently tolerated; in 2.12 it raises:

PydanticSerializationError: Error calling function `_serialize_refs`:
TypeError: 'index_key' is expected to be an integer or a string,
got 'SerializationInfo(...)'

Fix: serializer(self, info) → serializer(self) in base_data_class.py.

Closes: #45