perf(urlencoded): move empty-body guard to avoid extra function closure

[Phillip9587]

Inlines the empty-body check into the parser returned by createQueryParser, removing the extra wrapper function. The behavior is unchanged but we get a minor perf/alloc win by not creating a extra closure.

[Copilot]

Pull Request Overview

This PR optimizes the URL-encoded body parsing by eliminating an extra function closure and moving the empty-body check directly into the parser function. The change improves performance by removing an unnecessary wrapper function while maintaining identical behavior.

• Moves empty-body guard from wrapper function to main parser function
• Eliminates extra function closure creation
• Changes var to const for the parser assignment

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