chore: add CODEOWNERS and LICENSE headers

[okramarenko]

No description provided.

[cursor]

PR Summary

Low Risk
Primarily adds/standardizes file headers and CODEOWNERS with no functional behavior changes expected. Low risk aside from potential tooling/linting sensitivity to header formatting in SQL/Jinja macros.

Overview
Adds a repository-wide CODEOWNERS file and standard Apache 2.0 copyright/license headers across the SingleStore adapter Python modules, dbt macros (Jinja/SQL), example jaffle_shop project files, and test suite files.

Also introduces header-only stubs for a couple of package/test init files (and macros/utils/data_types.sql) to ensure consistent licensing coverage.

^{Reviewed by Cursor Bugbot for commit a7c993d. Configure here.}