[CI] Improve linters and git hooks

[testableapple]

Resolve https://linear.app/stream/issue/IOS-321

🎯 Goal

We introduced a new approach to git hooks on Feeds and fixed linters' issues. The goal of this PR is to align this across all iOS repos.

🏄‍♂️ Local support

To update git hooks locally, run:

bundle install
bundle exec lefthook install

If you use Git GUI (e.g.: Fork), you have to let the GUI know about zsh PATH explicitly:

Summary by CodeRabbit

• Chores

  • Switched to Lefthook for managing Git hooks and automated code formatting in pre-commit.
  • Updated workflow automation to use Fastlane for Swift code formatting and linting.
  • Added Lefthook gem and configuration.
  • Removed custom scripts and manual Git hook setup in favor of Lefthook.
  • Removed SwiftLint build phases from the Xcode project.

• Style

  • Improved code formatting and whitespace in several files.
  • Added and adjusted SwiftLint directives for specific functions to manage linting rules.

• Documentation

  • No user-facing documentation changes.