Raise error when initial state shape is wrong

[stavros11]

Implements the fix described in #646 (comment) and closes #646.

Note that without this, the qibojit-numba backend will proceed with execution and return wrong results, sometimes with a non-normalized final state or segmentation fault.

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.84%. Comparing base (70901d5) to head (28da693).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1361   +/-   ##
=======================================
  Coverage   99.84%   99.84%           
=======================================
  Files          74       74           
  Lines       10760    10763    +3     
=======================================
+ Hits        10743    10746    +3     
  Misses         17       17           

Flag	Coverage Δ
unittests	99.84% <100.00%> (+<0.01%)	⬆️

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[scarrazza]

Thanks @stavros11.