✨[Feature] Upgrade `setup.py` Python-only install

[gs-olive]

Context

The current Python build system relies on particular files and directories which do not have C++ dependencies. This can lead to issues when there are mixed C++/Python functionalities in a user-specified way (for example TRTModule vs TRTModuleNext).

Feature Proposal

Update setup.py and relevant files in the FX + Dynamo directories to have "Python-only" versions of key functions, which can then be safely imported when a user builds the repository with a Python-only flag.

[github-actions]

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