Fix root_validator issues with optional fields and made meta optional

[ml-evs]

After some fiddling, it seems like all that needed to be done was set pre=True in the remaining root validators, otherwise "data" seems to get validated first and popped from the response dict? (unsure)

I've also had to make meta optional for EntryResponseOne and EntryResponseMany, which changes the openapi spec. I'm not sure how I feel about this...

[codecov]

Codecov Report

Merging #145 into master will not change coverage.
The diff coverage is 25%.

@@           Coverage Diff           @@
##           master     #145   +/-   ##
=======================================
  Coverage   85.79%   85.79%           
=======================================
  Files          39       39           
  Lines        1830     1830           
=======================================
  Hits         1570     1570           
  Misses        260      260

Flag	Coverage Δ
#unittests	85.79% <25%> (ø)	⬆️

Impacted Files	Coverage Δ
optimade/models/optimade_json.py	83.33% <ø> (ø)	⬆️
optimade/models/jsonapi.py	90% <ø> (ø)	⬆️
optimade/validator/validator.py	62.33% <25%> (ø)	⬆️

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[CasperWA]

After some fiddling, it seems like all that needed to be done was set pre=True in the remaining root validators, otherwise "data" seems to get validated first and popped from the response dict? (unsure)

Right! That makes sense - sort of :)

I've also had to make meta optional for EntryResponseOne and EntryResponseMany, which changes the openapi spec. I'm not sure how I feel about this...

This is fine. meta is OPTIONAL after all, with respect to the spec.

[CasperWA]

Very good fix. Thanks @ml-evs.

I have only a small change request for consistency.

[CasperWA]

Very good fix. Thanks @ml-evs.

I have only a small change request for consistency.

I have just pushed the fix myself - I hope you agree with it as well? I will just wait for your input and otherwise merge it.

[ml-evs]

Cheers @CasperWA, I've just been even pickier with the language :P Hope you still accept!

[CasperWA]

Great with extra nit-picky pickyness @ml-evs 😅