Export synchronous wget functions

[rodolpheh]

This PR adds wget and wget_data which are wrappers to Emscripten's emscripten_wget and emscripten_wget_data. To use them, ASYNCIFY should be enabled.

[Copilot]

Pull Request Overview

This PR exports synchronous wget functions by adding Zig wrappers around Emscripten's emscripten_wget and emscripten_wget_data functions for downloading files and data synchronously.

• Adds wget function for downloading files to the local filesystem
• Adds wget_data function for downloading data directly into memory
• Requires ASYNCIFY to be enabled for synchronous operation

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