feat(pgsql): ✨ Add templates for constraints and sequences

* Introduce new templates for creating unique, check, and foreign key constraints with existence checks.
* Add templates for setting sequence values and creating sequences.
* Refactor existing SQL generation logic to utilize new templates for better maintainability and readability.
* Ensure identifiers are properly quoted to handle special characters and reserved keywords.

pkg/writers/pgsql/template_functions.go

@@ -21,6 +21,7 @@ func TemplateFunctions() map[string]interface{} {
 		"quote":           quote,
 		"escape":          escape,
 		"safe_identifier": safeIdentifier,
+		"quote_ident":     quoteIdent,
 
 		// Type conversion
 		"goTypeToSQL": goTypeToSQL,
@@ -122,6 +123,43 @@ func safeIdentifier(s string) string {
 	return strings.ToLower(safe)
 }
 
+// quoteIdent quotes a PostgreSQL identifier if necessary
+// Identifiers need quoting if they:
+// - Start with a digit
+// - Contain special characters
+// - Are reserved keywords
+// - Contain uppercase letters (to preserve case)
+func quoteIdent(s string) string {
+	if s == "" {
+		return `""`
+	}
+
+	// Check if quoting is needed
+	needsQuoting := unicode.IsDigit(rune(s[0]))
+
+	// Starts with digit
+
+	// Contains uppercase letters or special characters
+	for _, r := range s {
+		if unicode.IsUpper(r) {
+			needsQuoting = true
+			break
+		}
+		if !unicode.IsLetter(r) && !unicode.IsDigit(r) && r != '_' {
+			needsQuoting = true
+			break
+		}
+	}
+
+	if needsQuoting {
+		// Escape double quotes by doubling them
+		escaped := strings.ReplaceAll(s, `"`, `""`)
+		return `"` + escaped + `"`
+	}
+
+	return s
+}
+
 // Type conversion functions
 
 // goTypeToSQL converts Go type to PostgreSQL type