ESLint config format is deprecated

[MajorLift]

• The config format that we currently use is deprecated starting in ESLint v9: https://eslint.org/docs/latest/use/configure/configuration-files-deprecated
• The @metamask/eslint-config monorepo has migrated to the new flat config format, which makes it necessary for all downstream repos that use @metamask/-namespaced configs to perform this migration as well.
  • https://github.com/MetaMask/eslint-config/issues/362
  • https://github.com/MetaMask/eslint-config/pull/370
• Analogous PR in ts-bridge that can serve as a reference: https://github.com/ts-bridge/ts-bridge/pull/63