translator: add toolUse support in streaming

[wengyao04]

In this PR, I convert toolUse in bedrock converse streaming response to openai chat completions tool_calls. ToolUseBlockDelta is added toConverseStreamEventContentBlockDelta as documented in ContentBlockDelta. ContentBlockStart is added as documented in ContentBlockStart

The role in ChatCompletionResponseChunkChoiceDelta is not nullable as documented in https://platform.openai.com/docs/api-reference/chat/streaming

Unit test is updated to cover streaming response with toolUse. The base64 encoded streaming test data if from calling bedrock anthropic Claude model with toolConfig.

[mathetake]

looks good to me in general, so deferring to Dan for the rest

[mathetake]

so i made it easy to add the end-to-end transformation testing with testupstream here:

ai-gateway/tests/extproc/testupstream_test.go

Line 54 in b1b23e2

for _, tc := range []struct {

feel free to add more cases to cover this PR (maybe some fix might be necessary for the test as well as testupstream)

[wengyao04]

so i made it easy to add the end-to-end transformation testing with testupstream here:

ai-gateway/tests/extproc/testupstream_test.go

Line 54 in b1b23e2

for _, tc := range []struct {

feel free to add more cases to cover this PR (maybe some fix might be necessary for the test as well as testupstream)

Thank you, I will add more test cases to cover this PR and previous one for toolCalls