fix: monitor objects and delete property

[Nanosync]

Fixes #217

This PR ensures changed in Session is set to true by:

• observing modifications to objects (and recursive objects) within Session
• observing when the delete keyword is used within Session (and recursive objects)

Checklist

• [x] run npm run test and npm run benchmark
• [x] tests and/or benchmarks are included
• [ ] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct

[mcollina]

I still don't understand why it needs to be in module scope vs inside the plugin scope.

[Nanosync]

@mcollina Do you mean that sessionProxyCache should be moved into the scope of fastifySecureSession? I was not aware that fastifySecureSession would be called multiple times.

Edit: I've moved its scope.

[mcollina]

I'm not sure why but the tests are now failing, I'm reverting.

https://github.com/fastify/fastify-secure-session/actions/runs/8631175011/job/23659036483#step:5:117

Feel free to open a fresh PR with this, but these kind of failures are why I generically prefer to avoid Proxy.