Raw results and metadata

[thisac]

Context: There's no way to access non-samples results (i.e., metadata) in the Result class.

Description of the Change:

• A Result.raw method is added that returns the raw result dictionary.
• A Result.metadata method is added that returns the metadata of the results (i.e., everything except the "output" entry).
• Tests are added for the Result class.
• A setter method is added for Result.state allowing a state to be set iff a state has not previously been set and the Result object contains samples_dict samples, indicating that it's a local simulation.

Benefits:

• Results metadata can be accessed without using the private Result._result method.
• The Result class is properly tested.
• The state can be properly set in the result object.

Possible Drawbacks:

• The state setter relies on the fact that all local simulations have a samples_dict (which is currently the case).

Related GitHub Issues: None

[codecov[bot]]

Codecov Report

Merging #663 (13aade4) into master (e8c1403) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #663   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files          72       72           
  Lines        8815     8824    +9     
=======================================
+ Hits         8664     8673    +9     
  Misses        151      151           

Impacted Files	Coverage Δ
...trawberryfields/backends/bosonicbackend/backend.py	100.00% <100.00%> (ø)
strawberryfields/engine.py	95.91% <100.00%> (-0.02%)	:arrow_down:
strawberryfields/ops.py	98.30% <100.00%> (ø)
strawberryfields/result.py	94.73% <100.00%> (+1.87%)	:arrow_up:

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[heltluke]

Gotta love f-strings :heart: