fix: update copilot.Blob to copilot.AttachmentTypeBlob and fix Python Optional codegen

- Update Go E2E test, README, and docs to use prefixed enum constant
- Fix Python codegen modernizePython to handle deeply nested Optional types
- Fix ruff formatting in e2e/test_multi_client.py

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

docs/features/image-input.md

@@ -315,7 +315,7 @@ func main() {
 		Prompt: "Describe what you see in this image",
 		Attachments: []copilot.Attachment{
 			{
-				Type:        copilot.Blob,
+				Type:        copilot.AttachmentTypeBlob,
 				Data:        &base64ImageData,
 				MIMEType:    &mimeType,
 				DisplayName: &displayName,
@@ -333,7 +333,7 @@ session.Send(ctx, copilot.MessageOptions{
     Prompt: "Describe what you see in this image",
     Attachments: []copilot.Attachment{
         {
-            Type:        copilot.Blob,
+            Type:        copilot.AttachmentTypeBlob,
             Data:        &base64ImageData, // base64-encoded string
             MIMEType:    &mimeType,
             DisplayName: &displayName,

test/scenarios/prompts/attachments/README.md

@@ -39,7 +39,7 @@ Demonstrates sending **file attachments** alongside a prompt using the Copilot S
 |----------|------------------------|
 | TypeScript | `attachments: [{ type: "blob", data: base64Data, mimeType: "image/png" }]` |
 | Python | `"attachments": [{"type": "blob", "data": base64_data, "mimeType": "image/png"}]` |
-| Go | `Attachments: []copilot.Attachment{{Type: copilot.Blob, Data: &data, MIMEType: &mime}}` |
+| Go | `Attachments: []copilot.Attachment{{Type: copilot.AttachmentTypeBlob, Data: &data, MIMEType: &mime}}` |
 
 ## Sample Data