Refactor into multi-package mono-repo

[sillychipmunk]

Summary

• Extract generic tower-hs core library with protocol-agnostic Service/Middleware abstractions and middleware (retry, timeout, circuit breaker, filter, hedge, test doubles)
• Add generic middleware to tower-hs:
  • Tower.Middleware.Tracing — configurable OTel spans with request/response/error attribute hooks
  • Tower.Middleware.Logging — timed logging with user-provided formatter
  • Tower.Middleware.Validate — generic response validation
  • Tower.Middleware.Transform — generic request transformation (withMapRequest, withMapRequestPure)
• Refactor http-tower-hs into a thin HTTP wrapper depending on tower-hs — SetHeader, RequestId, Validate, Tracing, Logging all use generic building blocks
• Add servant-tower-hs with:
  • Adapter bridging tower-hs middleware to servant's ClientMiddleware type
  • Servant-specific middleware: SetHeader, RequestId, Validate, Tracing, Logging (operating on servant's Request/Response types, also built on generic building blocks)
  • Integration tests combining generic + servant-specific middleware in one stack
  • OTel tracing integration tests with in-memory exporter + real warp server
• Add Redis testcontainer integration test in tower-hs proving generic middleware works with non-HTTP services
• Add standalone example apps in examples/:
  • example-http-client — HTTP client with combined generic + HTTP middleware
  • example-servant-client — Servant client with combined generic + servant middleware
  • example-generic-redis — Redis client demonstrating non-HTTP use case
• Hackage readiness: per-package LICENSE, README.md, CHANGELOG.md, extra-doc-files, version bounds on tower-hs dep, Paths_* for OTel libraryVersion
• Rename HttpError to TransportError for protocol-agnostic naming
• Add shared Tower.Error.Testing module with Eq ServiceError instance (eliminates 9 orphan instances)
• Network.HTTP.Tower re-exports everything for backwards compatibility

Test plan

• stack test tower-hs — 55 tests passing (including 6 Redis Docker integration tests)
• stack test http-tower-hs — 44 tests passing
• stack test servant-tower-hs — 29 tests passing (including OTel tracing + combined middleware stack)
• stack test — all 128 tests passing
• stack sdist — all 3 packages produce clean tarballs with zero warnings
• stack run example-http-client — works
• CI workflow runs successfully on all GHC versions (9.6.6, 9.8.4, 9.10.1)

[jarlah]

Add test in tower-hs for using the middlewares for something else like database health queries
Edit: Done

[jarlah]

Also need to check if all packages are ready for Hackage. And, if they are independently useful. Im considering an examples folder for tower-hs, servant and http. How it will actually look like using the three libraries
edit: done