feat(wasm): implement single-file WebAssembly build for improved web compatibility

[abretonc7s]

Description

Overview

This PR implements a new build process that consolidates WebAssembly output into a single file, improving compatibility for web environments and preparing the groundwork for React Native integration with sherpa-onnx.

Changes

• Created a new build script for generating a combined WebAssembly output
• Updated README documentation to reflect the new build process and output locations

Purpose

The primary goal of these changes is to improve web compatibility by consolidating the WebAssembly build into a single file. This work is foundational for creating a React Native wrapper for sherpa-onnx, which will provide full web compatibility across platforms.

Technical Details

• The WebAssembly build now generates a single file output that encapsulates all necessary functionality
• Build artifacts are properly excluded from version control
• Documentation has been updated to reflect the new build and output structure

Breaking Changes

None. This change maintains backward compatibility while adding new functionality.

Migration Steps

No migration steps are required for existing implementations.