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/claude/openai/chat-completions/init.go

@@ -0,0 +1,19 @@
+package chat_completions
+
+import (
+	. "github.com/luispater/CLIProxyAPI/internal/constant"
+	"github.com/luispater/CLIProxyAPI/internal/interfaces"
+	"github.com/luispater/CLIProxyAPI/internal/translator/translator"
+)
+
+func init() {
+	translator.Register(
+		OPENAI,
+		CLAUDE,
+		ConvertOpenAIRequestToClaude,
+		interfaces.TranslateResponse{
+			Stream:    ConvertClaudeResponseToOpenAI,
+			NonStream: ConvertClaudeResponseToOpenAINonStream,
+		},
+	)
+}