fix: function_call can be a string or an object

[j178]

According to the document, function_call parameter can a string literal: "none", "auto", or an object with a key "name".

https://platform.openai.com/docs/api-reference/chat/create#chat/create-function_call

Also added FunctionCall to ChatCompletionStreamChoiceDelta.

[codecov]

Codecov Report

Merging #374 (158fa4e) into master (0bd14f9) will increase coverage by 0.85%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master     #374      +/-   ##
==========================================
+ Coverage   95.22%   96.08%   +0.85%     
==========================================
  Files          17       17              
  Lines         670      689      +19     
==========================================
+ Hits          638      662      +24     
+ Misses         22       19       -3     
+ Partials       10        8       -2     

Impacted Files	Coverage Δ
chat.go	96.77% <93.33%> (-3.23%)	⬇️
chat_stream.go	100.00% <100.00%> (+10.71%)	⬆️

... and 1 file with indirect coverage changes

[vvatanabe]

Also added FunctionCall to ChatCompletionStreamChoiceDelta.

Oops, it's a specification that the arguments are returned in stream!

data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"{\n"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":" "}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":" \""}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"location"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"\":"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":" \""}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"Boston"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"\"\n"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{"function_call":{"arguments":"}"}},"finish_reason":null}]}
data: {"id":"chatcmpl-***","object":"chat.completion.chunk","created":1686862207,"model":"gpt-3.5-turbo-0613","choices":[{"index":0,"delta":{},"finish_reason":"function_call"}]}
data: [DONE]

[vvatanabe]

How about adding a structure as a usable type?
For example:

type Foo struct {
	Name string `json:"name"`
}

[jabalsad]

Anything I can do to help push this PR forward?

[j178]

Sorry, I'm not available to push this forward, so closing. Please take #388 a look instead.