feat(mssql): add MSSQL writer for generating DDL from database schema

- Implement MSSQL writer to generate SQL scripts for creating schemas, tables, and constraints.
- Support for identity columns, indexes, and extended properties.
- Add tests for column definitions, table creation, primary keys, foreign keys, and comments.
- Include testing guide and sample schema for integration tests.

pkg/mssql/README.md

@@ -0,0 +1,99 @@
+# MSSQL Package
+
+Provides utilities for working with Microsoft SQL Server data types and conversions.
+
+## Components
+
+### Type Mapping
+
+Provides bidirectional conversion between canonical types and MSSQL types:
+
+- **CanonicalToMSSQL**: Convert abstract types to MSSQL-specific types
+- **MSSQLToCanonical**: Convert MSSQL types to abstract representation
+
+## Type Conversion Tables
+
+### Canonical → MSSQL
+
+| Canonical | MSSQL | Notes |
+|-----------|-------|-------|
+| int | INT | 32-bit signed integer |
+| int64 | BIGINT | 64-bit signed integer |
+| int32 | INT | 32-bit signed integer |
+| int16 | SMALLINT | 16-bit signed integer |
+| int8 | TINYINT | 8-bit unsigned integer |
+| bool | BIT | 0 (false) or 1 (true) |
+| float32 | REAL | Single precision floating point |
+| float64 | FLOAT | Double precision floating point |
+| decimal | NUMERIC | Fixed-point decimal number |
+| string | NVARCHAR(255) | Unicode variable-length string |
+| text | NVARCHAR(MAX) | Unicode large text |
+| timestamp | DATETIME2 | Date and time without timezone |
+| timestamptz | DATETIMEOFFSET | Date and time with timezone offset |
+| uuid | UNIQUEIDENTIFIER | GUID/UUID type |
+| bytea | VARBINARY(MAX) | Variable-length binary data |
+| date | DATE | Date only |
+| time | TIME | Time only |
+| json | NVARCHAR(MAX) | Stored as text (MSSQL v2016+) |
+| jsonb | NVARCHAR(MAX) | Stored as text (MSSQL v2016+) |
+
+### MSSQL → Canonical
+
+| MSSQL | Canonical | Notes |
+|-------|-----------|-------|
+| INT, INTEGER | int | Standard integer |
+| BIGINT | int64 | Large integer |
+| SMALLINT | int16 | Small integer |
+| TINYINT | int8 | Tiny integer |
+| BIT | bool | Boolean/bit flag |
+| REAL | float32 | Single precision |
+| FLOAT | float64 | Double precision |
+| NUMERIC, DECIMAL | decimal | Exact decimal |
+| NVARCHAR, VARCHAR | string | Variable-length string |
+| NCHAR, CHAR | string | Fixed-length string |
+| DATETIME2 | timestamp | Default timestamp |
+| DATETIMEOFFSET | timestamptz | Timestamp with timezone |
+| DATE | date | Date only |
+| TIME | time | Time only |
+| UNIQUEIDENTIFIER | uuid | UUID/GUID |
+| VARBINARY, BINARY | bytea | Binary data |
+| XML | string | Stored as text |
+
+## Usage
+
+```go
+package main
+
+import (
+    "fmt"
+    "git.warky.dev/wdevs/relspecgo/pkg/mssql"
+)
+
+func main() {
+    // Convert canonical to MSSQL
+    mssqlType := mssql.ConvertCanonicalToMSSQL("int")
+    fmt.Println(mssqlType) // Output: INT
+
+    // Convert MSSQL to canonical
+    canonicalType := mssql.ConvertMSSQLToCanonical("BIGINT")
+    fmt.Println(canonicalType) // Output: int64
+
+    // Handle parameterized types
+    canonicalType = mssql.ConvertMSSQLToCanonical("NVARCHAR(255)")
+    fmt.Println(canonicalType) // Output: string
+}
+```
+
+## Testing
+
+Run tests with:
+```bash
+go test ./pkg/mssql/...
+```
+
+## Notes
+
+- Type conversions are case-insensitive
+- Parameterized types (e.g., `NVARCHAR(255)`) have their base type extracted
+- Unmapped types default to `string` for safety
+- The package supports SQL Server 2016 and later versions