feat: remove root-level import of all modules in python

[DanielMSchmidt]

In python importing a submodule leads to all __init__.py files below the import path being executed. We have an index.ts with a namespaced import for all submodules as an entry point for JSII (It needs to be there so all the submodules are being registered). This leads to a from a provider point of view top-level __init__.py importing all the namespaces, so even if users use specific submodule imports they import the entire provider.

This change cuts the synth time in half for the AWS example (from 30s to 15s).

This is a breaking change since top-level imports (from imports.aws import s3Bucket) don't work anymore, they need to be replaced with namespace imports (from imports.aws.s3_bucket import S3Bucket).

Additionally this PR upgrades JSII and JSII-Srcmak, allowing us to use the new lazy loading mechanism within JSII bringing the initial synth time down from 15s to 5s and every iterative synth (after the providers and modules are in the JSII cache) down to 2s.

TL;DR: Breaking change bringing Pythons synth time down from 30s to 2s

[ansgarm]

Looking good! Only a small typo and a question.

As this is a breaking change, I think we should add an unreleased section to the changelog and give some before & after examples for this change. Upon the next release, we should also copy that to an upgrade guide (not sure if adding an upgrade guide already would release it too soon 😄)

[github-actions]

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