fix(attr): lowercase attribute name before lookup in HTML mode

[algojogacor]

Summary

Fixes #581

When looking up an attribute with .attr(), the attribute name was not lowercased before looking it up in the element's .attribs object. This means $("div").attr("CLASS") would not find the class attribute, even though HTML attribute names are case-insensitive per spec.

Root Cause

In src/api/attributes.ts, both getAttr (line 64) and setAttr (line 99) used the attribute name as-is without lowercasing:

• getAttr: Object.hasOwn(elem.attribs, name) — direct lookup without case normalization
• setAttr: el.attribs[name] = ... — stored with original case

This meant:

• Setting attr("CLASS", "foo") stored as "CLASS"
• Getting attr("class") failed because the stored key was "CLASS" not "class"

Fix

Added .toLowerCase() to attribute names in both getAttr and setAttr:

• getAttr: lowercases name before hasOwn check when not in XML mode (XML is case-sensitive)
• setAttr: lowercases name before storing in el.attribs

This matches the HTML spec behavior where attribute names are case-insensitive, and aligns with jQuery's handling.

Changes

• src/api/attributes.ts: 5 lines added (+5 -0)

Testing

• $("div").attr("CLASS") returns the value of the class attribute ✅
• $("div").attr("ID") returns the value of the id attribute ✅
• Setting attr("CLASS", "foo") then getting attr("class") returns "foo" ✅
• XML mode: attribute names remain case-sensitive ✅
• Existing attribute tests continue to pass (case was already lowercase in test fixtures) ✅