WIP: Initial code for aiosqlite and base async backend

[Andrew-Chen-Wang]

Adding async backend Base and aiosqlite -- someone else can pick it up if I become inactive.

• Adds aatomic and an async atomic
• Adds alru_cache
• Internal django test cases can skip if it's an async or sync backend.

aatomic probably shouldn't have been implemented in this PR, but I also couldn't think of another time it could be implemented without a Base async backend.

There is no associated ticket as of yet. This was made a month ago, but because I could never pick this up due to classes, I made a PR for others to take advantage of. I should have time after February 20th to get back to this.

To write transaction test cases, it requires the async ORM.

[Andrew-Chen-Wang]

Can't seem to figure out why the socket is not being closed (assuming this is the async side):

Exception ignored in: <socket.socket fd=3, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 58768), raddr=('127.0.0.1', 58766)>
ResourceWarning: unclosed <socket.socket fd=3, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('127.0.0.1', 58768), raddr=('127.0.0.1', 58766)>

[Shankar-Balaji-U]

from channels.db import database_sync_to_async

@database_sync_to_async
def get_user(mobile_no):
	return MyModel.objects.get(mobile_no=mobile_no)


user = get_user("9999999999")

it's works fine!!!

[felixxm]

Closing due to inactivity.