fix(translator): address PR feedback for tool name sanitization

- Pre-compile sanitization regex for better performance.
- Optimize SanitizeFunctionName for conciseness and correctness.
- Handle 64-char edge cases by truncating before prepending underscore.
- Fix bug in Antigravity translator (incorrect join index).
- Refactor Gemini translators to avoid redundant sanitization calls.
- Add comprehensive unit tests including 64-char edge cases.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

internal/translator/gemini/claude/gemini_claude_request.go

@@ -100,11 +100,12 @@ func ConvertClaudeRequestToGemini(modelName string, inputRawJSON []byte, _ bool)
 						if toolCallID == "" {
 							return true
 						}
-						funcName := util.SanitizeFunctionName(toolCallID)
+						rawFuncName := toolCallID
 						toolCallIDs := strings.Split(toolCallID, "-")
 						if len(toolCallIDs) > 1 {
-							funcName = util.SanitizeFunctionName(strings.Join(toolCallIDs[0:len(toolCallIDs)-1], "-"))
+							rawFuncName = strings.Join(toolCallIDs[0:len(toolCallIDs)-1], "-")
 						}
+						funcName := util.SanitizeFunctionName(rawFuncName)
 						responseData := contentResult.Get("content").Raw
 						part := `{"functionResponse":{"name":"","response":{"result":""}}}`
 						part, _ = sjson.Set(part, "functionResponse.name", funcName)