Add nvfuser to requirements.txt

## 🚀 Feature
Today, nvfuser requirements a manual install. It is NOT part of requirements.txt.
Ideally users should be able to get all default executors without having to go through the README.MD and then manually install them.

### Motivation

This is a followup task for discussion on #427. [LINK to thread](https://github.com/Lightning-AI/lightning-thunder/pull/427#discussion_r1603988364)

### Pitch
Add `nvfuser-cu121[torch]` to requirements/base.txt.

CC @IvanYashchuk @t-vi

Start with requirements/base.txt and review the linked discussion on PR #427 for the dependency context. Add the requested nvfuser-cu121[torch] entry, then verify that the requirements file includes the default executor dependency without requiring the manual README installation step.

Written by the indexing model from the issue text.