Fixes Distributive-Network#208

Implement isolated JavaScript execution contexts in PythonMonkey.

* Define `Context` class in `include/modules/pythonmonkey/pythonmonkey.hh` to encapsulate JSContext, global object, auto realm, and job queue.
* Implement `Context` class in `src/modules/pythonmonkey/pythonmonkey.cc` for initialization, destruction, and accessing the context.
* Add `createContext`, `evalInContext`, and `cleanupContexts` functions in `src/modules/pythonmonkey/pythonmonkey.cc` to manage multiple contexts.
* Update `eval` function in `src/modules/pythonmonkey/pythonmonkey.cc` to accept a context ID and evaluate JavaScript code within the specified context.
* Update module initialization in `src/modules/pythonmonkey/pythonmonkey.cc` to include the `context` function.
* Add `SuperGlobalContext` class in `include/modules/pythonmonkey/pythonmonkey.hh` to encapsulate shared JSContext, global object, auto realm, and job queue.
* Implement `SuperGlobalContext` class in `src/modules/pythonmonkey/pythonmonkey.cc` for initialization and cleanup of shared resources.
* Update `Context` class to reference `SuperGlobalContext` for shared resources.
* Modify `evalInContext` function to use `SuperGlobalContext` for shared resources.
* Make `SuperGlobalContext` accessible through a `GLOBAL_CX` variable.
* Update `JobQueue` class in `include/JobQueue.hh` and `src/JobQueue.cc` to accept a JSContext in the constructor.
* Update various proxy classes in `src/JSMethodProxy.cc`, `src/JSObjectItemsProxy.cc`, `src/JSObjectIterProxy.cc`, `src/JSObjectKeysProxy.cc`, `src/JSObjectProxy.cc`, and `src/JSStringProxy.cc` to use the `Context` object instead of the global `GLOBAL_CX` variable.