Update ESLint and related packages (including TypeScript ESLint support for TS 5.9.x)

[coderabbitai]

Summary

Upgrade ESLint and all related linting packages to their latest compatible versions. This is a follow-up from PR #188 (comment: #188 (comment)), which pinned TypeScript to 5.9.3 but left ESLint tooling on older, incompatible versions.

Motivation

• @typescript-eslint/eslint-plugin and @typescript-eslint/parser are currently at ^5.29.0, which does not support TypeScript 5.9.x. Only @typescript-eslint 8.39.0 and later officially support TypeScript 5.9.x. Running npm run lint currently emits an unsupported TypeScript version warning.
• eslint is currently on ^8.57.1 (ESLint v8 is end-of-life). Upgrading to ESLint v9+ and aligning all plugins is desirable.

Packages to update

Package	Current version	Action
@typescript-eslint/eslint-plugin	^5.29.0	Upgrade to ^8.39.0 or latest 8.x
@typescript-eslint/parser	^5.29.0	Upgrade to ^8.39.0 or latest 8.x
eslint	^8.57.1	Upgrade to latest (v9.x)
eslint-config-prettier	^8.5.0	Upgrade to latest
eslint-plugin-prettier	^4.1.0	Upgrade to latest
eslint-plugin-react	^7.30.1	Upgrade to latest
eslint-plugin-react-hooks	^4.6.0	Upgrade to latest
eslint-plugin-simple-import-sort	^7.0.0	Upgrade to latest
eslint-plugin-testing-library	^5.6.0	Upgrade to latest

Notes

• Moving to ESLint v9 requires migrating the ESLint configuration to the flat config format (eslint.config.js). This may involve additional effort.
• Verify all lint rules still pass after the upgrade and adjust the ESLint config as needed.

Requested by

@vojtechszocs