perf: `is_followed_by` take too long for the current user

[uukelele]

when i go to the page for a user while i'm logged in - scratch.mit.edu/users/username, it immediately shows the "Follow" / "Unfollow" button. in the HTML you can see this:

<div class="follow-button button following grey" data-control="unfollow"> <!-- THIS-->
	<span class="follow text"><span class="icon-sm follower white"></span>Follow</span>
	<span class="unfollow text"><span class="icon-sm follower black"></span>Unfollow</span>
</div>

on initial load, so i'm assuming that data-control will tell the JS which element to hide?

for a user that i'm not currently following it shows as this:

<div class="follow-button button notfollowing blue" data-control="follow">
	<span class="follow text"><span class="icon-sm follower white"></span>Follow</span>
	<span class="unfollow text"><span class="icon-sm follower black"></span>Unfollow</span>
</div>

so this confirms my suspicions, the data-control is an effective way to tell if you are following a scratcher or not.

but right now the code I use to do this:

user.is_followed_by(me.username)

for a user that i follow with only 19 followers total to iterate through, the function took 61.36 seconds to run¹ (benchmarked with time.time)

edit: SEE FOOTNOTE, behaviour is inconsistent
in fact see the description of PR for timing details

i think it's better if we have a separate function (or attribute?) on the User class to tell if the connected user is being followed or not by the current user, maybe .is_followed_by_me()

Footnotes

1. i have no idea why it took that long when i looked through the code it doesn't seem like it should take too long especially for a user with 19 followers means only one iteration ... maybe ratelimiting? i doubted myself here so after about ~10 minutes of no activity on the API i reran the code and still 52 seconds .. not sure what's going on. edit: it's been an hour now and i retried and somehow it's now 0.2 seconds for the exact same user!?!!? ↩

[uukelele]

i will solve in #572