Rewrite missing blocks range query

[vbaranov]

Motivation

Function to find missing blocks ranges in given range misses some ranges.

For instance, current implementation of missing_block_number_ranges function returns empty range for this range Explorer.Chain.missing_block_number_ranges(12859384..12859386) even though _4 is not consensus block, _5 is missing.

dai=# select consensus, number from blocks where number in (12859383, 12859384, 12859385, 12859386);
 consensus |  number
-----------+----------
 t         | 12859383
 f         | 12859384
 t         | 12859386
(3 rows)

Changelog

Fully rewrite the query and add tests which don't work with the previous algorithm.

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build b8e184f8389b14b2dceba9033d6eeff48ff9fda9-PR-3440

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.08%) to 67.433%

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Totals
Change from base Build f3e4e0081c2f67a2f3f51fb0803476364aaf15e8:	-0.08%
Covered Lines:	2054
Relevant Lines:	3046

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💛 - Coveralls