Add nvfuser to requirements.txt

[vedaanta]

🚀 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

Pitch

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

CC @IvanYashchuk @t-vi

[mruberry]

triage review —

• we should consider cpu-only builds (even if they are only for development)
• maybe there's an additional .txt file we can provide so people can opt-in to installing nvfuser