test(unit): add unit tests for untested source files

[Chemaclass]

🤔 Background

Several core source files had zero unit tests, leaving gaps in the test suite coverage.

💡 Changes

• Add 6 new unit test files covering env.sh, math.sh, colors.sh, test_title.sh, console_header.sh, and doc.sh
• Use data providers to efficiently test all 21 boolean env flag checkers in both true/false states
• Add dedicated tests for special-case functions like find_terminal_width fallback, active_internet_connection network opt-out, and math::calculate fallback paths
• Total: 71 new tests bringing the suite from ~847 to 918

[github-actions]

✅ Contributor Report

User: @Chemaclass
Status: Trusted contributor (whitelisted)

This user is on the trusted contributors list and was automatically approved.