fix: resolve 2 bugs in leetcode-ranking

[saurabhhhcodes]

Description

This PR fixes real bugs found in the codebase:

• Replaced global isNaN with Number.isNaN: the global version coerces its argument, so isNaN('1') returns false while Number.isNaN is strict.
• Switched innerText to textContent: textContent is deterministic and faster since it skips layout recalc.

Type of Change

• Bug fix (non-breaking change fixing an issue)

How Has This Been Tested?

• Local manual testing

Checklist

• My code follows the style guidelines
• I have performed a self-review

Related Issue

Ref: #393

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