Add comprehensive XML documentation for public APIs

[Copilot]

This PR adds comprehensive XML documentation to the SQLProvider's public APIs to significantly improve the developer experience and reduce the learning curve for new users.

What was added

Core SQL Operators and Types (Operators.fs):

• ConditionOperator - SQL conditional operators (LIKE, IN, etc.) with clear explanations
• AggregateOperation - SQL aggregate functions (SUM, COUNT, etc.)
• CanonicalOp - SQL functions for strings, dates, and math operations
• Custom operators like |=|, |<>|, =%, <>%, !! with usage examples
• SelectOperations - Query execution location control

Database Schema Types (SqlSchema.fs):

• TypeMapping - Database to .NET type mapping with field explanations
• QueryParameter - SQL parameter metadata for stored procedures
• Column - Table column information including constraints and data types
• Relationship - Foreign key relationships for navigation properties
• Table - Database table representation with quoting support

SSDT/DacPac Support (Ssdt.DacpacParser.fs):

• Module overview explaining SSDT .dacpac file parsing capabilities
• Core data types for representing SQL Server schema elements
• extractModelXml - Extract schema from .dacpac files
• parseXml - Parse SSDT model.xml content with namespace support

Runtime and Core Types (SqlRuntime.Common.fs):

• DatabaseProviderTypes - All supported database providers with descriptions
• ISqlDataContext - Main data context interface documenting all CRUD operations
• EntityState - Entity change tracking for SubmitUpdates operations
• OnConflict - UPSERT conflict resolution strategies
• QueryEvents.SqlQueryEvent - SQL execution monitoring for debugging

Async and Transaction Support:

• AsyncOperations - Non-blocking query execution functions
• IsolationLevel - Database isolation levels with detailed explanations
• TransactionOptions - Transaction configuration options

Benefits

• Better IDE Support: Comprehensive tooltips and IntelliSense
• Reduced Learning Curve: Clear explanations of complex concepts like operators and isolation levels
• Improved Debugging: Documentation for monitoring events and async operations
• Usage Examples: Practical code examples for complex operators and attributes
• API Clarity: Clear parameter and return value descriptions

The documentation follows F# XML documentation standards and focuses on APIs that users directly interact with, making SQLProvider more accessible to both new and experienced developers.

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