Speed up build

[penguinland]

Without this PR, it takes about 65 seconds on my Orin Nano to run make setup, which was the preferred way to build the module. With this PR, you only need to run make setup once at the very beginning, and then running make build (or make dist/module.tar.gz, or even just make) goes about 25 seconds faster than it used to. It's still slower than I'd like, but the wait is more tolerable...

Tried both in the clone of the repo I've been developing on and a brand new clone, seems to work on both.

[kharijarrett]

I might be wrong but it seems like this makes some actual changes. Doesn't seem like we're activating or doing anything inside a virtual environment anymore. Is that intended/are we cool with that?

[penguinland]

Before this PR, you had to activate the venv before running any of the make commands. I said to myself "let's have the make commands activate the venv so you don't need to do it yourself," and it worked great locally. but then the Github CI said "there is no venv, we've installed everything globally (within your ephemeral container), so all checks have failed!" So, I took it out again, and you need to activate the venv yourself just like before.

[penguinland]

(compare the way the second-most-recent commit failed its checks, and then the most recent one passes them)