Add ros2_medkit packages

[baradejoo]

Goal

Add the ros2_medkit diagnostic stack to the robostack-jazzy distribution.

Description

ros2_medkit (https://index.ros.org/r/ros2_medkit/) is a structured diagnostic model for ROS 2 robots that exposes faults over a REST/SOVD API. This PR adds the released 0.4.0 packages: the message/service interfaces, the fault manager and detection, the diagnostic/log/action bridges, the REST gateway SOVD plugins.

The dependency libcpp-httplib-dev is mapped to the conda-forge cpp-httplib package (used by the gateway's REST server).

Changes

• Added the ros2_medkit packages to the jazzy build selection in vinca.yaml.
• Added a rosdep mapping libcpp-httplib-dev -> cpp-httplib in robostack.yaml.
• Added a patch fixing a std::vector<bool> build error in
  ros2_medkit_serialization on macOS (see Notes).

License

ros2_medkit is licensed under Apache-2.0 (per the upstream packages).

Notes

Build tested locally on osx-arm64.

macOS (serialization): ros2_medkit_serialization failed to compile on clang/libc++ with:
error: implicit instantiation of undefined template 'YAML::convert<std::__bit_const_reference<std::vector<bool>>>'. The vendored dynmsg code pushes a std::vector<bool>::operator[] proxy directly into a yaml-cpp node; clang has no conversion for that proxy type. Fixed with a one-line patch casting the proxy to bool before push_back (patch/ros-jazzy-ros2-medkit-serialization.patch). This is a genuine upstream bug (present in 0.4.0 through main).

[baradejoo]

Summary of platform status

After testing ros2_medkit on all platforms, there are a few upstream portability issues worth flagging before this is ready for review. tl;dr: everything builds on linux-64; the gateway stack is blocked on the other platforms for different reasons, each described below.

Version (0.6.0 via additional_recipes)

The jazzy snapshot pins ros2_medkit 0.4.0, which doesn't build against conda-forge's current cpp-httplib 0.51: the gateway used httplib::Request::get_file_value, removed from httplib after ~0.18. Upstream rewrote this to the MultipartFormData API in 0.6.0, so I pull in 0.6.0 via rosdistro_additional_recipes.yaml (which overrides the snapshot and is manually maintained, so it survives a snapshot regeneration) rather than editing the auto-generated rosdistro_snapshot.yaml. @traversaro @Tobias-Fischer — is that the right mechanism for a version override, or would you prefer another approach?

linux-aarch64 — only blocked by cpp-httplib

The only blocker on linux-aarch64 is that conda-forge doesn't ship cpp-httplib for ARM — the feedstock (https://github.com/conda-forge/cpp-httplib-feedstock) only builds linux-64, osx-64 and win-64. pipe2 and dlfcn.h are both available on linux-aarch64, so once cpp-httplib is available for linux-aarch64, the whole stack (including the gateway) should build on both linux-64 and linux-aarch64 with no further changes here. Since cpp-httplib is header-only, adding ARM should be straightforward. @wolfv, as the feedstock maintainer — would you be open to that?

macOS (osx-64 / osx-arm64) — pipe2 is Linux-only

The gateway fails on macOS with:

default_script_provider.cpp:437: error: use of undeclared identifier 'pipe2'
`pipe2()` is a Linux-specific extension; macOS/BSD only has `pipe()`. 

The gateway uses it unconditionally (plus a few other POSIX-only headers), so it can't build on macOS as-is — this is independent of the cpp-httplib issue so even with httplib on osx-arm64 the gateway would still need a pipe2 fix.

Windows — dlfcn.h is POSIX-only

ros2_medkit_serialization vendors dynmsg, whose typesupport.cpp includes <dlfcn.h> and uses dlopen/dlsym/dlclose with no Windows fallback, so it fails on MSVC with:

typesupport.cpp(16): error C1083: Cannot open include file: 'dlfcn.h'

Since serialization is a core dependency, this blocks most of the stack on win-64.

Note on package count

index.ros.org lists 19 ros2_medkit packages for jazzy, but only 16 are actually bloomed to ros2-gbp/ros2_medkit-release — fault_detection, graph_watchdog and opcua have no release tag, so this PR adds the 16 available ones.

[wolfv]

I can take care of cpp-httplib!