Add ingress-client API with typed reqwest clients, docs, and integration coverage

[robertream]

Summary

Adds a new ingress-client capability to the Rust SDK with a typed reqwest-based client API, macro-generated typed ingress clients, and runtime/compile-time test coverage.

Included in this commit

New ingress client module

• Added src/ingress.rs with:
  • Client
  • ServerUrl (+ TryFrom conversions)
  • AuthToken
  • Request<Res>
  • RequestError
• Request customization support:
  • headers
  • idempotency key
  • timeout
  • delay query parameter

Macro-generated typed ingress clients

• Updated macros/src/generator.rs to generate typed ingress client impls for services, objects, and workflows.
• Generated ingress interfaces use request-oriented trait naming (Into*Request, Request<'a>, create_request).

Crate exports

• Updated src/lib.rs and feature wiring so ingress client APIs are available behind ingress-client.

Tests

• Added tests/ingress.rs runtime coverage for ingress behavior, including:
  • typed service/object/workflow invocation
  • auth token validation
  • status propagation
  • idempotency header propagation
  • serialize failure propagation
  • delay=...ms query serialization
• Updated compile/UI tests for feature-gated ingress paths:
  • tests/compiletest.rs
  • tests/ui/ingress-client/*

Testcontainers

• Added ingress-client feature forwarding in testcontainers/Cargo.toml.
• Updated testcontainers/tests/test_container.rs to include a feature-gated typed ingress client integration path alongside the existing HTTP-based one.

Documentation

• Added module-level ingress docs and typed usage examples.
• Added API docs for ingress structs/methods and RequestError variants.
• Added/updated doctests for key ingress entry points.

Validation

• cargo test -q
• cargo test --features ingress-client -q
• cargo test -p restate-sdk-testcontainers --no-run
• cargo test -p restate-sdk-testcontainers --features ingress-client --no-run

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[robertream]

I hadn't read the original issue and PR from a year ago. I updated the implementation to support the "executor" API that was suggested.

[robertream]

I have read the CLA Document and I hereby sign the CLA

[tillrohrmann]

Thanks a lot for creating this PR @robertream. It's quite a piece of work you have contributed 👏 We will probably need a little bit of time for reviewing your design and the code. Having typed clients for Rust would be kick-ass :-)

cc @slinkydeveloper for your input.