Refactor translator packages for OpenAI Chat Completions

- Renamed `openai` packages to `chat_completions` across translator modules.
- Introduced `openai_responses_handlers` with handlers for `/v1/models` and OpenAI-compatible chat completions endpoints.
- Updated constants and registry identifiers for OpenAI response type.
- Simplified request/response conversions and added detailed retry/error handling.
- Added `golang.org/x/crypto` for additional cryptographic functions.

internal/translator/gemini/openai/chat-completions/gemini_openai_request.go

@@ -1,6 +1,6 @@
 // Package openai provides request translation functionality for OpenAI to Gemini API compatibility.
 // It converts OpenAI Chat Completions requests into Gemini compatible JSON using gjson/sjson only.
-package openai
+package chat_completions
 
 import (
 	"fmt"

internal/translator/gemini/openai/chat-completions/gemini_openai_response.go

@@ -3,7 +3,7 @@
 // JSON format, transforming streaming events and non-streaming responses into the format
 // expected by OpenAI API clients. It supports both streaming and non-streaming modes,
 // handling text content, tool calls, reasoning content, and usage metadata appropriately.
-package openai
+package chat_completions
 
 import (
 	"bytes"

internal/translator/gemini/openai/chat-completions/init.go

@@ -1,4 +1,4 @@
-package openai
+package chat_completions
 
 import (
 	. "github.com/luispater/CLIProxyAPI/internal/constant"