feat: return mutation as object that does not need to be reparsed

[Taepper]

See loculus-project/loculus#1446

[fengelniederhammer]

I was about to bring up that discussion anyway, I really like the change 👍

In LAPIS we will most probably keep the old mutation field for backwards compatibility and convenience. Do we want to do the same here? Or do we rather want to strip the redundant data from the SILO responses?

[Taepper]

That is a good point, just returning both might be viable. What do you think @chaoran-chen. Keeping both fields only in LAPIS or also in SILO?

[fengelniederhammer]

(Also just to keep in mind: this PR should not be merged without preparation in LAPIS if it still contains breaking changes.)

[Taepper]

Similar to GenSpectrum/LAPIS#710 it might be better to include both in SILO, then we can order by all fields that are also returned by LAPIS

[Taepper]

Should be ready to merge now, as it is non-breaking for LAPIS. (auto-merge will act after tests passed and approving review)

[Taepper]

Some QOL changes introduced to query.test.js, where the actual result is directly written to a file that can be easier compared and copied