jit model init

[PhilipVinc]

This should speed-up the initialisation (Creation of variational state) for very large models, because under jit we won't be evaluating the output (instead without jit it is evaluated and then discarded).
It will add a tiny slowdown to initialisation for smaller models.

[github-actions]

Hello and thanks for your Contribution!
I will be building previews of the updated documentation at the following link:
https://netket.github.io/netket/preview/pv/jit

Once the PR is closed or merged, the preview will be automatically deleted.

[codecov-commenter]

Codecov Report

Merging #832 (d0ba9ad) into master (2d4432b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #832   +/-   ##
=======================================
  Coverage   79.08%   79.08%           
=======================================
  Files         162      162           
  Lines        9778     9778           
  Branches     1366     1366           
=======================================
  Hits         7733     7733           
  Misses       1684     1684           
  Partials      361      361           

Impacted Files	Coverage Δ
netket/vqs/mc_state.py	82.97% <100.00%> (ø)

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