feat: add CSV and JSON import/export functionality with extension methods

- Add WorksheetDataExtensions class with ImportFromCsv/Json and ExportToCsv/Json methods
- Implement CsvOptions and JsonOptions configuration classes with comprehensive settings
- Support nested JSON flattening, array conversion, and data type auto-detection
- Add robust CSV parsing with text qualifiers, custom delimiters, and encoding support
- Include comprehensive error handling and cell reference parsing utilities
- Add demo programs and test cases for validation

Author: fahadadeel

Excel/CsvOptions.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Text;
+
+namespace Openize.Cells
+{
+    /// <summary>
+    /// Configuration options for CSV import and export operations.
+    /// </summary>
+    public class CsvOptions
+    {
+        /// <summary>
+        /// Gets or sets whether the first row contains headers.
+        /// </summary>
+        public bool HasHeaders { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets the delimiter character used to separate values.
+        /// </summary>
+        public string Delimiter { get; set; } = ",";
+
+        /// <summary>
+        /// Gets or sets the text qualifier character (e.g., quote character).
+        /// </summary>
+        public string TextQualifier { get; set; } = "\"";
+
+        /// <summary>
+        /// Gets or sets the date format for parsing date values.
+        /// </summary>
+        public string DateFormat { get; set; } = "yyyy-MM-dd";
+
+        /// <summary>
+        /// Gets or sets the number format culture (e.g., "en-US", "de-DE").
+        /// </summary>
+        public string Culture { get; set; } = "en-US";
+
+        /// <summary>
+        /// Gets or sets whether to skip empty lines during import.
+        /// </summary>
+        public bool SkipEmptyLines { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets whether to trim whitespace from values.
+        /// </summary>
+        public bool TrimWhitespace { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets the encoding for reading/writing the CSV file.
+        /// </summary>
+        public Encoding Encoding { get; set; } = Encoding.UTF8;
+
+        /// <summary>
+        /// Gets or sets the maximum number of rows to import (0 = no limit).
+        /// </summary>
+        public int MaxRows { get; set; } = 0;
+
+        /// <summary>
+        /// Gets or sets whether to auto-detect data types.
+        /// </summary>
+        public bool AutoDetectDataTypes { get; set; } = true;
+    }
+}

Excel/JsonOptions.cs

@@ -0,0 +1,66 @@
+using System;
+
+namespace Openize.Cells
+{
+    /// <summary>
+    /// Configuration options for JSON import and export operations.
+    /// </summary>
+    public class JsonOptions
+    {
+        /// <summary>
+        /// Gets or sets whether to include property names as headers in the first row.
+        /// </summary>
+        public bool IncludeHeaders { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets the date format for parsing and formatting date values.
+        /// </summary>
+        public string DateFormat { get; set; } = "yyyy-MM-dd";
+
+        /// <summary>
+        /// Gets or sets the date-time format for parsing and formatting datetime values.
+        /// </summary>
+        public string DateTimeFormat { get; set; } = "yyyy-MM-dd HH:mm:ss";
+
+        /// <summary>
+        /// Gets or sets whether to auto-detect data types during import.
+        /// </summary>
+        public bool AutoDetectDataTypes { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets the number format culture (e.g., "en-US", "de-DE").
+        /// </summary>
+        public string Culture { get; set; } = "en-US";
+
+        /// <summary>
+        /// Gets or sets whether to ignore null or empty values during import.
+        /// </summary>
+        public bool IgnoreNullValues { get; set; } = false;
+
+        /// <summary>
+        /// Gets or sets the maximum number of records to import (0 = no limit).
+        /// </summary>
+        public int MaxRecords { get; set; } = 0;
+
+        /// <summary>
+        /// Gets or sets whether to flatten nested objects into columns with dot notation.
+        /// Example: {"user": {"name": "John"}} becomes "user.name" column.
+        /// </summary>
+        public bool FlattenNestedObjects { get; set; } = false;
+
+        /// <summary>
+        /// Gets or sets the separator for flattened nested object property names.
+        /// </summary>
+        public string NestedPropertySeparator { get; set; } = ".";
+
+        /// <summary>
+        /// Gets or sets whether to handle arrays by converting them to comma-separated strings.
+        /// </summary>
+        public bool ConvertArraysToStrings { get; set; } = true;
+
+        /// <summary>
+        /// Gets or sets the separator for array values when converting to strings.
+        /// </summary>
+        public string ArrayValueSeparator { get; set; } = ", ";
+    }
+}