Add JavaScript as a language target

[Copilot]

Adds JavaScript code generation that produces human-readable CommonJS modules, reusing patterns from the TypeScript generator.

Code Generator

• src/struct_frame/js_gen.py - Generates .sf.js files with CommonJS require/module.exports syntax
• Boilerplate files in src/struct_frame/boilerplate/js/ for struct serialization, framing, and parsing

CLI Integration

• Added --build_js and --js_path flags to generate.py

Test Infrastructure

• JavaScript test suite in tests/js/ mirroring TypeScript tests
• Updated test_config.json with JavaScript language configuration
• Modified tests/runner/base.py and plugins.py to handle JS test execution from generated directory

Usage

PYTHONPATH=src python3 src/main.py myproto.proto --build_js --js_path gen/js

Generated output:

const { Struct } = require('./struct_base');
const { msg_encode } = require('./struct_frame');

const basic_types_BasicTypesMessage = new Struct('basic_types_BasicTypesMessage')
    .Int8('small_int')
    .UInt16LE('medium_uint')
    .String('device_id', 32)
    .compile();
module.exports.basic_types_BasicTypesMessage = basic_types_BasicTypesMessage;

All 74 tests pass including cross-platform compatibility between C, C++, Python, TypeScript, and JavaScript.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add Javascript as a language</issue_title>
<issue_description>This generator and tests should reuse a lot of the code from the typescript tests. One of the languages can act as a wrapper. There is also js being created, if this js is being used it needs to still be human readable. </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add Javascript as a language #32

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