chore(deps): update ESLint to v10 and its plugins to their new majors

[GraemeF]

Moves the repo to ESLint 10 with eslint-plugin-functional 10 and typescript-eslint 8.71. The rules enforced on the repo are unchanged.

• The three unused plugins are removed instead of upgraded. No ESLint config in the repo loads eslint-plugin-compat, eslint-plugin-package-json or eslint-plugin-expect-type. knip never reported them, because knip.json ignores every eslint-plugin-* dependency. Say if you want any of them back.
• @codeforbreakfast/eslint-effect works under ESLint 10 now. ESLint 10 removed context.getSourceCode(), which most of its rules called. Its eslint peer range moves from >=8.0.0 to >=8.40.0, the first release with context.sourceCode. One rule already needed 8.40.
• One lock entry was refreshed by hand. The lockfile held is-immutable-type 5.0.1 with its own copy of typescript-eslint 8.44, which crashes on load under ESLint 10. Deleting that entry let Bun resolve 5.0.4 against the shared typescript-eslint 8.71.
• eslint-plugin-functional 10 now reports Record<…> parameters and return types as mutable. The fix wraps them in Readonly<…>, in the WebSocket server and in scripts/validate-changesets.ts.
• eslint-plugin-import stays on 2.32.0. Its peer range stops at ESLint 9, and it has no newer release. The one rule the repo uses, import/extensions, reports the same violation under ESLint 9 and 10.

[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