Decrease loaders showing delay on the main page

[vbaranov]

Motivation

Loaders showing delay on the main page was set to 1 second #2324, what is too long. It was decreased to 100 ms. It means if the data will not be fetched from the server in 100 ms, mock loaders will be shown.

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 d1907bb0-d559-4e3b-af6a-91d143fe4f06

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+1.1%) to 76.18%

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Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	1	78.57%

Totals
Change from base Build d297bed9-74f4-4fd1-8c38-77caeacadae6:	1.1%
Covered Lines:	5357
Relevant Lines:	7032

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💛 - Coveralls