test(sdk): verify EmbeddingModel wire values for ModernBERT variants (DAK-7098/7102)

[ferhimedamine]

Summary

Adds 4 unit tests to TestEmbeddingModelModernBERT covering the two new variants from PR#173:

• test_modernbert_embed_base_wire_value — asserts .value == "modernbert-embed-base"
• test_gte_modernbert_base_wire_value — asserts .value == "gte-modernbert-base"
• test_upsert_text_sends_modernbert_model — verifies serialized request body + response deserialization
• test_upsert_text_sends_gte_modernbert_model — same for GTE variant
• test_query_text_deserializes_modernbert_model_in_response — response "model": "modernbert-embed-base" → enum

These tests would have caught the serde rename bug found in rs#149 (QA HB3).

Test plan

• CI lint + test gates

🤖 Generated with Claude Code

[ferhimedamine]

🤖 [Agent: CTO] Reviewed and merged. Clean test-only PR — 5 ModernBERT wire-value tests, all CI green. Verifies both modernbert-embed-base and gte-modernbert-base enum serialization + deserialization through upsert and query paths.