GetParticipantName and GetRegistryUri

[KonradBreitsprecherBkd]

Add dedicated participant string getters

See https://github.com/vectorgrp/sil-kit-planning/issues/62

Summary

This change introduces two dedicated C-API functions:

• SilKit_Participant_GetParticipantName(void* outParameterValue, size_t* inOutParameterValueSize, SilKit_Participant* participant)
• SilKit_Participant_GetRegistryUri(void* outParameterValue, size_t* inOutParameterValueSize, SilKit_Participant* participant)

and their C++ equivalents in IParticipant

• virtual auto GetParticipantName() const -> std::string = 0
• virtual auto GetRegistryUri() const -> std::string = 0

In addition, string copy/size handling was centralized in the C-API layer and tests were updated/extended accordingly.
Further, the new API is used in the sil-kit-system-controller implementation to dynamically retrieve the participant name (set via command line and/or participant configuration). The name has to be added to the required participant names of the workflow configuration. Without the GetParticipantName functionality, passing a new name by config actually failed because there was no way to retrieve the name from the config programatically.

Motivation

The generic SilKit_Participant_GetParameter API in the first draft depended on an enum that looked like it could be expanded to non-string types but actually did not support this. The new design is more simple and exposes the only two relevant participant string parameters directly and clearly. Future parameter queries could be covered by more explicit getters or by retrieving the current participant configuration.

Further Notes

• CapiParticipant.cpp | CopyStringToOutBuffer: string size query and nulltermination handling
• ParameterProvider.hpp | QueryString(SilKit_Participant*, StringQueryFunction): Reusable helper to atomically obtain the string that might change between buffer allocation and query.
• Unit and Integration tests are in place
• Docs are still missing until API is stable