Remove fragile error handling from sendChatHistory methods

[Copilot]

Addresses feedback on #157 regarding fragile err.message.includes('is required') string check in error handling. This pattern is brittle and unnecessary since sendChatHistory already implements proper error contracts.

Changes

• Removed try-catch blocks with string-based error detection from sendChatHistoryAsync and sendChatHistoryMessagesAsync
• Removed unused import of OperationError
• Simplified control flow to let validation errors propagate naturally while runtime errors return as OperationResult

Before

try {
  return await this.configService.sendChatHistory(
    turnContext,
    chatHistoryMessages,
    effectiveOptions
  );
} catch (err) {
  if (err instanceof Error && err.message.includes('is required')) {
    throw err;
  }
  return OperationResult.failed(new OperationError(err as Error));
}

After

return await this.configService.sendChatHistory(
  turnContext,
  chatHistoryMessages,
  effectiveOptions
);

The underlying sendChatHistory method already throws validation errors and returns OperationResult.failed() for HTTP/runtime failures, making the catch block redundant.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.