Add support for emscripten laz compression

[but0n]

This PR adds a LazWriter class for managing LAZ file writing in the browser.

JavaScript Example:

...
const writer = new Module.LazWriter()
    .setPointFormat(pointFormat)
    .setTransform(
        header_info.offset.x,
        header_info.offset.y,
        header_info.offset.z,
        header_info.scale.x,
        header_info.scale.y,
        header_info.scale.z,
    );
writer.open(
    output.ptr,
    output.size,
);
for (var i = 0; i < pointCount; ++i) {
    laszip.getPoint(pointbuf.ptr);
    writer.writePoint(pointbuf.ptr);
}
const actual_size = writer.close();
const filebuf = output.resize(Number(actual_size)).to_owned_buffer();
const blob = new Blob([filebuf.buffer], { type: 'application/octet-stream' });
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'output.laz';
link.click();
URL.revokeObjectURL(url);

Additionally, the PR updates the CMakeLists.txt to include:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s WASM_BIGINT -s EXPORTED_FUNCTIONS=['_malloc, _free']")

This ensures that symbols like _malloc and _free, which were previously exported from native code for internal use, are explicitly exported to the Module object. These changes were made necessary due to an Emscripten update from about a year ago (ChangeLog).

Let me know if you need any adjustments!