improvements(ai): Improve AI streaming UI/UX interactions + better separation of AI provider responsibilities (#2039)

* Start refactor

* Interface updates

* Rework Assistant, Provider, and tests for better domain boundaries

* Consolidate and simplify OpenAI provider and provider concepts

* Clean up assistant streaming

* Improve assistant message orchestration logic

* Clean up "thinking" UI interactions

* Remove stale class

* Regenerate VCR test responses

test/vcr_cassettes/openai/chat/error.yml

@@ -5,8 +5,7 @@ http_interactions:
     uri: https://api.openai.com/v1/responses
     body:
       encoding: UTF-8
-      string: '{"model":"invalid-model-that-will-trigger-api-error","input":[{"role":"user","content":"Error
-        test"}],"instructions":null,"tools":[],"previous_response_id":null,"stream":true}'
+      string: '{"model":"invalid-model-that-will-trigger-api-error","input":[{"role":"user","content":"Test"}],"instructions":null,"tools":[],"previous_response_id":null,"stream":null}'
     headers:
       Content-Type:
       - application/json
@@ -24,7 +23,7 @@ http_interactions:
       message: Bad Request
     headers:
       Date:
-      - Wed, 26 Mar 2025 21:27:19 GMT
+      - Mon, 31 Mar 2025 20:38:55 GMT
       Content-Type:
       - application/json
       Content-Length:
@@ -36,25 +35,25 @@ http_interactions:
       Openai-Organization:
       - "<OPENAI_ORGANIZATION_ID>"
       X-Request-Id:
-      - req_2b86e02f664e790dfa475f111402b722
+      - req_3981f27aa18db734b3dd530fa2929b95
       Openai-Processing-Ms:
-      - '146'
+      - '113'
       Strict-Transport-Security:
       - max-age=31536000; includeSubDomains; preload
       Cf-Cache-Status:
       - DYNAMIC
       Set-Cookie:
-      - __cf_bm=gAU0gS_ZQBfQmFkc_jKM73dhkNISbBY9FlQjGnZ6CfU-1743024439-1.0.1.1-bWRoC737.SOJPZrP90wTJLVmelTpxFqIsrunq2Lqgy4J3VvLtYBEBrqY0v4d94F5fMcm0Ju.TfQi0etmvqZtUSMRn6rvkMLmXexRcxP.1jE;
-        path=/; expires=Wed, 26-Mar-25 21:57:19 GMT; domain=.api.openai.com; HttpOnly;
+      - __cf_bm=8KUMK_Gp4f97KLactyy3QniUZbNmN9Zwbx9WowYCc98-1743453535-1.0.1.1-opjT17tCwi9U0AukBXoHrpPEcC4Z.GIyEt.AjjrzRWln62SWPIvggY4L19JabZu09.9cmxfyrwAFHmvDeCVxSWqAVf88PAZwwRICkZZUut0;
+        path=/; expires=Mon, 31-Mar-25 21:08:55 GMT; domain=.api.openai.com; HttpOnly;
         Secure; SameSite=None
-      - _cfuvid=XnxX4KU80himuKAUavZYtkQasOjXJDJD.QLyMrfBSUU-1743024439792-0.0.1.1-604800000;
+      - _cfuvid=uZB07768IynyRRP6oxwcnC4Rfn.lGT1yRhzzGvNw0kc-1743453535322-0.0.1.1-604800000;
         path=/; domain=.api.openai.com; HttpOnly; Secure; SameSite=None
       X-Content-Type-Options:
       - nosniff
       Server:
       - cloudflare
       Cf-Ray:
-      - 9269bb3b2c14cf74-CMH
+      - 9292a7327d5161d6-ORD
       Alt-Svc:
       - h3=":443"; ma=86400
     body:
@@ -68,5 +67,5 @@ http_interactions:
             "code": "model_not_found"
           }
         }
-  recorded_at: Wed, 26 Mar 2025 21:27:19 GMT
+  recorded_at: Mon, 31 Mar 2025 20:38:55 GMT
 recorded_with: VCR 6.3.1