Fix the linter

[jlwllmr]

Describe the bug

The linter currently won't run on any PR:

ESLint: 8.57.1

Error [ERR_MODULE_NOT_FOUND]: Cannot find package '@eslint/compat' imported from /Users/Work/Documents/GitHub/doc.linea/eslint.config.mjs
    at packageResolve (node:internal/modules/esm/resolve:844:9)
    at moduleResolve (node:internal/modules/esm/resolve:901:20)
    at defaultResolve (node:internal/modules/esm/resolve:1131:11)
    at ModuleLoader.defaultResolve (node:internal/modules/esm/loader:390:12)
    at ModuleLoader.resolve (node:internal/modules/esm/loader:359:25)
    at ModuleLoader.getModuleJob (node:internal/modules/esm/loader:234:38)
    at ModuleWrap.<anonymous> (node:internal/modules/esm/module_job:85:39)
    at link (node:internal/modules/esm/module_job:84:36)

@eslint/compat was installed as part of the changes in #708, where we moved to the new ES module formatting for the linter config files. This format is required for eslint 9.x.x, but the plugins that we use with eslint are not compatible with eslint 9.x.x, so we still have it at 8.57.x.

As far as I can see, we need to either:

1. Gradually remove the eslint plugins and see if it the linter still works (side quest: identify precisely what each of them actually offers)
2. Revert back to the CommonJS config format and stay at eslint 8.56.x/8.57.x

Steps to reproduce

npm run lint

Expected behavior

Linter should run.

Link(s)

No response