fix: Fail on unknown PostgreSQL types instead of defaulting to string (fixes #30)

[richardwooding]

Summary

Fixes #30 - Type Provider now fails fast on unknown PostgreSQL types instead of silently defaulting to string.

Problem

Previously, FindStructFieldType() defaulted unknown PostgreSQL types (UUID, INET, geometric types, custom enums) to decls.String, causing:

• ❌ Incorrect SQL generation (wrong operators for type)
• ❌ Type mismatches in comparisons
• ❌ Silent failures that are hard to debug

Solution

1. Added Explicit Support for Common PostgreSQL Types

• UUID → decls.Bytes
• INET, CIDR → decls.String (network addresses)
• MACADDR, MACADDR8 → decls.String (MAC addresses)
• XML → decls.String
• MONEY → decls.Double
• TSVECTOR, TSQUERY → decls.String (full-text search)

2. Changed Default Behavior

Unknown PostgreSQL types now return found=false instead of defaulting to string. This provides:

• ✅ Clear errors at type provider creation
• ✅ Prevention of silent type mismatches
• ✅ Better type safety and debugging

3. Comprehensive Testing

• Added Test_typeProvider_PostgreSQLTypes with 13 test cases
• Tests all newly supported types
• Tests arrays of new types
• Tests unknown types correctly return found=false

4. Updated Documentation

• Reorganized CLAUDE.md Type System Integration section
• Documented all supported PostgreSQL types by category
• Added note about unsupported types behavior

Breaking Change ⚠️

Code using unsupported PostgreSQL types (e.g., point, polygon, box, custom enums) will now fail at type provider creation instead of silently converting to string.

Migration: Add explicit support for custom types or use composite type definitions in your schema.

Testing

• ✅ All existing tests pass
• ✅ All new tests pass
• ✅ Full test suite: go test ./... passes

Checklist

• Code follows project conventions
• Tests added for new functionality
• Documentation updated
• All tests passing
• Breaking change documented

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