feat: add --type-map to override SQL-to-Go types in bun and gorm writers

Adds WriterOptions.TypeMappings and a repeatable --type-map sqltype=gotype
flag. Defaults are unchanged when no mapping is given. Closes #36 (bun/gorm).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

pkg/writers/writer.go

@@ -83,6 +83,13 @@ type WriterOptions struct {
 	// SqlXxxArray wrapper types.
 	NullableArrays string
 
+	// TypeMappings overrides the SQL-to-Go type mapping of the code-generation
+	// writers (bun, gorm). Keys are SQL base types (aliases are canonicalized,
+	// see ParseTypeMappings), values are Go type expressions. Array columns
+	// use the override for their element type. Unmapped types keep the
+	// built-in defaults.
+	TypeMappings map[string]string
+
 	// Prisma7 enables Prisma 7-specific output for Prisma writers.
 	Prisma7 bool