fix: resolve codeformatter test failures and compilation errors

[vuon9]

Summary

This PR fixes multiple test failures and a compilation error in the internal/codeformatter package:

• Fixed compilation error: Variable html was shadowing the html package import in css_selector_test.go
• Fixed test expectations: Changed literal \n to actual newline characters in test assertions
• Fixed CSS descendant selector: Rewrote selector logic to properly respect ancestor relationships and added deduplication
• Fixed XML attribute matching: Updated to handle attributes in any order (not just immediately after tag name)
• Fixed nested XML extraction: Corrected test to properly count elements using slice method

Changes

New Features

• Added support for element.class selectors (e.g., div.header)
• Added support for double quotes in XPath expressions (e.g., //book[@id="bk101"])
• Added proper handling for direct child (>) vs any descendant (space) selectors

Bug Fixes

• Fixed findElementsByDescendant to properly parse and execute chained selectors
• Fixed extractElementByAttribute to search attributes regardless of order
• Fixed applyXPathFilter to recognize double-quoted attribute values

Test Plan

• All Go tests pass (go test ./...)
• CSS selector tests cover element, class, ID, descendant, and element.class selectors
• XPath filter tests cover element selection, attribute matching, and nested paths
• XML extraction tests properly count elements

Testing

go test ./...

All 8 test packages passing ✅

[github-actions]

Package	Line Rate	Health
devtoolbox/internal/barcode	90%	✔
devtoolbox/internal/codeformatter	78%	➖
devtoolbox/internal/converter	60%	➖
devtoolbox/internal/datagenerator	91%	✔
devtoolbox/internal/datetimeconverter	73%	➖
devtoolbox/internal/jwt	42%	❌
devtoolbox/internal/settings	0%	❌
Summary	68% (3504 / 5175)	➖

Minimum allowed line rate is 60%