Add OslcRequestParams and graph accumulation support to OslcClient

[Copilot]

Addresses #325: Enables configurable request parameters and graph accumulation in OslcClient, properly resolving #19 and #204 (header overwriting issues).

Changes

• OslcRequestParams class — Configures Accept, Content-Type, OSLC-Core-Version, and custom headers. Supports merge semantics for per-request overrides.

  • Pre-built configs: Default, RdfXmlOnly, TurtleOnly
  • Fluent Builder() API

• Graph accumulation — EnableGraphAccumulation() / DisableGraphAccumulation() for discovery phase workflows where responses should merge into a single graph

• Per-request parameter overrides — New overloads for GetResourceAsync and CreateResourceAsync accepting OslcRequestParams

• DefaultRequestParams property — Set globally in constructor or per-request

Usage

// Constructor-level defaults
var client = new OslcClient(logger, OslcRequestParams.RdfXmlOnly);

// Per-request override
var customParams = OslcRequestParams.Builder()
    .WithAccept("text/turtle")
    .WithHeader("X-Custom", "value")
    .Build();
await client.GetResourceAsync<ServiceProvider>(uri, null, customParams);

// Discovery with graph accumulation
var graph = client.EnableGraphAccumulation();
await client.GetResourceAsync<ServiceProviderCatalog>(catalogUri);
await client.GetResourceAsync<ServiceProvider>(spUri);
// graph now contains merged triples from both responses

Notes

• OslcRestClient remains deprecated (since 0.5.0)
• 21 new unit tests added
• All existing APIs unchanged

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Merge OslcClient and OslcRestClient</issue_title>
<issue_description>- [ ] Ensure #19 and #204 are solved properly. I am thinking of OslcRequestParams that we pre-set in the library, allow the user to set in the ctor, or to override on a per-request basis (mainly, to request/specify certain types, e.g. request only RDF/XML for root services or POST RDF/XML-ABBREV in some special cases)

• Allow access of both unmarshalled POCOs as well as access to the raw response graph.
• Allow the client to be set to accumulate the responses in a single graph - useful for the initial discovery phase.</issue_description>

<agent_instructions>OslcClient should remain. Increase test coverage during the join.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@berezovskyi OslcRestClient is largely deprecated since 0.5.0 - OslcClient is the primary client.

• Fixes Merge OslcClient and OslcRestClient #205

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.22%. Comparing base (97a6fca) to head (60c2153).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #468      +/-   ##
==========================================
+ Coverage   50.69%   51.22%   +0.53%     
==========================================
  Files         169      170       +1     
  Lines       10205    10309     +104     
  Branches     1017     1039      +22     
==========================================
+ Hits         5173     5281     +108     
+ Misses       4770     4761       -9     
- Partials      262      267       +5     

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