Add Host and ForwardedHost request extractors for hostname extraction

[aram356]

Resolves

• Closes Add Host extractor with X-Forwarded-Host support #21

Summary

• Add Host extractor that extracts the hostname from the standard Host header (falls back to "localhost" if not present)
• Add ForwardedHost extractor that prioritizes X-Forwarded-Host header over Host header for use behind reverse proxies/load balancers
• Fix clippy warnings by simplifying error handling patterns in tests (using .err().expect() instead of match statements)
• Add comprehensive test coverage for existing extractors (Query, Form, ValidatedQuery, ValidatedForm, ValidatedPath, Host, ForwardedHost)
• Add Deref/DerefMut and into_inner() tests for all extractor types

Test plan

• Unit tests added for Host extractor covering:
  • Extracts from Host header only
  • Ignores X-Forwarded-Host header
  • Defaults to "localhost" when no headers present
  • Deref and into_inner() functionality
• Unit tests added for ForwardedHost extractor covering:
  • X-Forwarded-Host takes priority over Host header
  • Falls back to Host header when X-Forwarded-Host is absent
  • Defaults to "localhost" when no host headers present
  • Deref and into_inner() functionality
• All existing tests pass

[ChristianPavilonis]

Looks pretty good 👍