Increase test coverage threshold for security-sensitive validators

[github-actions]

The global pytest coverage threshold is currently set to 80% (--cov-fail-under=80 in pyproject.toml). For security-sensitive modules like the validators/ package (e.g., blank_string_validator.py), this threshold may be insufficient — edge cases such as None, empty strings, whitespace-only values, and non-string types are security boundaries that should be fully exercised.

Suggested improvement: Raise the coverage requirement for validators/ modules to 95% or 100%, either via per-file coverage configuration or a separate pytest-cov run scoped to that package.

File: pyproject.toml, line 150

Review comment:

The coverage threshold of 80% may be insufficient for security-sensitive validation utilities like this blank string validator. Consider a higher threshold (e.g., 95% or 100%) for modules in the validators/ package, where comprehensive test coverage is critical to ensure all edge cases (None, empty strings, whitespace-only, valid strings) are exercised. Security boundaries should have near-complete test coverage.

Related PR: #51

Generated by PR Review Comment Handler for issue #51