Refactor CSV reader to support multiple files with improved concurrency performance

[HarrisChu]

• Added CsvReaderConfig struct for CSV reader configuration (Delimiter, WithHeader, Limit)
• Updated ICsvReader interface:
  • GetData(sourceFile string) (Data, error) - read from specified CSV file
  • Close() error - cleanup resources
• Added GetFileData(sourceFile string) (Data, error) to IGraphClient for backward compatibility

Usage

// Backward compatible - reads from default CSV (csv_path in options)
let d = session.getData()
// New - read from specific CSV files
let personData = session.getFileData("person.csv")
let companyData = session.getFileData("company.csv")