feat: Reverted order for indexed fields

[islamaliev]

Relevant issue(s)

Resolves #2229

Description

Enable reverted ordering for indexed fields. Which is mostly relevant to composite indexes.

This PR introduces a whole new package encoding. A significant part of it is taken from CocroachDB which fits well to our needs. Other encoding approaches (mostly for integers) were also consider: like fixed-length encoding, avro's zizzag encoding, base128 varints encoding and few others.

[codecov]

Codecov Report

Attention: Patch coverage is 88.63388% with 104 lines in your changes are missing coverage. Please review.

Project coverage is 75.05%. Comparing base (9248cbc) to head (ad348a8).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2335      +/-   ##
===========================================
+ Coverage    74.75%   75.05%   +0.30%     
===========================================
  Files          257      266       +9     
  Lines        25349    25855     +506     
===========================================
+ Hits         18949    19404     +455     
- Misses        5103     5147      +44     
- Partials      1297     1304       +7     

Flag	Coverage Δ
all-tests	75.05% <88.63%> (+0.30%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
client/document.go	70.64% <100.00%> (ø)
client/field.go	100.00% <100.00%> (+33.33%)	⬆️
client/index.go	80.95% <ø> (ø)
core/key.go	84.53% <100.00%> (-2.07%)	⬇️
db/collection_delete.go	32.77% <100.00%> (ø)
db/collection_index.go	90.85% <100.00%> (-0.16%)	⬇️
db/errors.go	61.09% <ø> (ø)
db/fetcher/encoded_doc.go	76.14% <100.00%> (ø)
db/index.go	67.92% <100.00%> (+0.96%)	⬆️
encoding/bytes.go	100.00% <100.00%> (ø)
... and 18 more

... and 8 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9248cbc...ad348a8. Read the comment docs.

[AndrewSisley]

Is going to take a while for me to get through this one :) Submitting first chunk of comments now.

[AndrewSisley]

Pausing my review for now - there appears to be a lot of dead code, and a lot of fairly fiddly and undocumented code. It looks like you have done a great job getting it to work, but I do not think it is yet ready for review.

Can you please remove the dead code, and document the remaining. Please in the code comments focus on why what is being done is being done.

[fredcarle]

I like the changes. I'm wondering if the encoding should eventually be applied to stored values instead of using cbor.

Approving with a few minor comments to resolve before merge.

it's discussed with him