Build wallet state asynchronously

[raphjaph]

Fixes #3061

Still need to clean this up.

@devords, @gmart7t2 Could you check if this makes things faster on your end?

[gmart7t2]

@devords, @gmart7t2 Could you check if this makes things faster on your end?

It's 11x faster than the master branch, but 11x slower than 0.15.0:

$ time echo $(ordr2-new balance) # origin/master
{ "cardinal": 3003000, "ordinal": 0, "total": 3003000 }

0m8.859s  0m9.030s  0m8.832s

$ time echo $(ordr2-new balance) # make-it-fast
{ "cardinal": 3003000, "ordinal": 0, "total": 3003000 }

0m0.676s  0m0.680s  0m0.714s

$ time echo $(ordr2 balance) # 0.15.0
{ "cardinal": 3003000, "ordinal": 0, "total": 3003000 }

0m0.052s  0m0.062s  0m0.072s

Trying with a bigger wallet, with 44 unspent outputs in it, and timing "wallet balance":

origin/master: 150s
make-it-fast: 5.3s
0.15.0: 0.15s

So make-it-fast is much faster than origin/master but much slower than 0.15.0.

[raphjaph]

@gmart7t2 Thanks for testing this, very helpful numbers!

I wasn't using async properly but now I am. Could you check if it is faster now?

[casey]

BACK TO THE DRAWING BOARD

[casey]

LGTM