feat(sdk): add LLM provider test & list-models enablers

[zdenekmusil-gd]

Add typed CatalogOrganizationService methods backed by ActionsApi so tooling can test connectivity and list models for LLM providers without using the raw api-client:

• test_llm_provider / test_llm_provider_by_id -> CatalogLlmProviderTestResult
• list_llm_provider_models / list_llm_provider_models_by_id -> CatalogLlmProviderModelsResult
• New result types parse responses with a casing-robust from_api, since the API returns nested result items as camelCase dicts
• Provider CRUD is unchanged

JIRA: GDAI-1811
risk: nonprod

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.10%. Comparing base (6e3ba76) to head (22b6da6).

Files with missing lines	Patch %	Lines
.../catalog/organization/entity_model/llm_provider.py	88.88%	3 Missing ⚠️
...k/src/gooddata_sdk/catalog/organization/service.py	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1634      +/-   ##
==========================================
+ Coverage   79.06%   79.10%   +0.04%     
==========================================
  Files         231      231              
  Lines       15667    15717      +50     
==========================================
+ Hits        12387    12433      +46     
- Misses       3280     3284       +4     

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