chore: migrates to eslint 9 & flat config

[sverweij]

Description

• bumps linting setup to eslint 9
• migrates (both) eslint configurations to 'flat config'
• The complexity calculation changed, so I've set the max allowed complexity a little bit higher (to 10; eslint's default is 20 (!) - previously we used 6).

Our eslint-config-moving-meadow configuration is still non-flat, so @eslint/migrate-config wrapped it in a compat call, which is fine for now.

Motivation and Context

eslint 8 is EOL and won't be supported any longer. An alternative till eslint 10 is setting the ESLINT_USE_FLAT_CONFIG environment variable to false, but that still made eslint emit a warning message on each run + we had to do the work anyway, eventually.

How Has This Been Tested?

• green ci

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Documentation only change
• Refactor (non-breaking change which fixes an issue without changing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore

Checklist

• 📖

  • My change doesn't require a documentation update, or ...
  • it does and I have updated it

• ⚖️

  • The contribution will be subject to The MIT license, and I'm OK with that.
  • The contribution is my own original work.
  • I am ok with the stuff in CONTRIBUTING.md.

[qlty-cloud-legacy]

Code Climate has analyzed commit b8009f0 and detected 0 issues on this pull request.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud