Add eslint-config-prettier to defer formatting rules to Prettier

[delthas]

What

• Append eslint-config-prettier as the last entry in eslint.config.mjs so it turns off the ESLint formatting rules Prettier owns (indent, max-len, …), and add it as a devDependency (^10).
• Remove the 4 max-len disable comments that become unused once max-len is off.
• The prettier-formatting of the touched files (eslint.config.mjs + the 2 files whose comments are removed) is isolated in a separate chore: commit so the logic commit shows only the config change.

This does not run Prettier over the whole codebase — only the files this change touches are formatted.

Why

Arsenal inherits both its ESLint rules and its Prettier config from @scality/eslint-config-scality. Several ESLint formatting rules conflict with Prettier's output. Since arsenal enabled the Prettier CI check (ARSN-558) — which runs prettier --check on the whole of each changed file — any PR that touches a previously-unformatted file is forced to Prettier-format it, which then fails yarn lint. The two checks impose opposite requirements and can't both be satisfied.

indent/max-len cannot be configured to match Prettier (Prettier exposes no equivalent knobs), so the ESLint rules must be disabled for Prettier-enforcing code. Appending eslint-config-prettier does exactly that. This is scoped to arsenal — repos that use the shared config without Prettier keep their formatting lints.

Scope

This is the per-repo half of the fix. The companion quote-props half — which can be reconciled by config — is handled upstream in the shared config by switching Prettier to quoteProps: 'consistent' (GDL-15, scality/Guidelines#213).

Context

• Full analysis and fix plan: https://scality.atlassian.net/wiki/x/CQDe8
• Upstream quote-props half: GDL-15 — Set Prettier quoteProps to consistent to match eslint quote-props Guidelines#213
• Unblocks: ARSN-572 (first PR to trip the deadlock).
• Mirrors the eslint↔prettier wiring from cloudserver CLDSRV-905: run prettier over the whole codebase cloudserver#6175 (CLDSRV-905). That PR also runs Prettier over the whole cloudserver codebase; here we deliberately extracted only the eslint-config-prettier part and left a whole-repo reformat for later.

Issue: ARSN-584

[bert-e]

Hello delthas,

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[bert-e]

Waiting for approval

The following approvals are needed before I can proceed with the merge:

• the author

• 2 peers

[claude]

LGTM

Review by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.51%. Comparing base (93c267f) to head (d45f288).

Additional details and impacted files

@@                 Coverage Diff                 @@
##           development/8.4    #2630      +/-   ##
===================================================
- Coverage            73.55%   73.51%   -0.05%     
===================================================
  Files                  222      222              
  Lines                18214    18214              
  Branches              3798     3798              
===================================================
- Hits                 13398    13390       -8     
- Misses                4811     4818       +7     
- Partials                 5        6       +1     

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