test: improve test coverage from 0% to 99% (#11)

Rewrite test suite with 68 tests covering all 4 source modules.
Mock Selenium, Playwright, and undetected_chromedriver at import
level so tests run without heavy browser dependencies. Cover
__main__ blocks via runpy. Add requests to test dependencies.

Author: GeiserX

requirements-test.txt

@@ -2,3 +2,4 @@ pytest>=7.0
 pytest-cov>=4.0
 beautifulsoup4
 lxml
+requests