fix: handle MT940 statement numbers longer than 5 digits

The MT940 standard expects statement numbers to be maximum 5 digits,
but some banks provide longer statement numbers that cause parsing errors.

Problem:
- MT940 files with statement numbers > 5 digits fail to parse
- Error: "Unable to parse StatementNumber object from '167619/1'"
- This breaks bank statement import functionality

Solution:
- Add preprocess_mt940_content() function to truncate long statement numbers
- Preserve sequence numbers (e.g., '/1') when present
- Apply preprocessing before mt940.parse() to ensure compatibility

The fix truncates statement numbers to the last 5 digits while maintaining
the MT940 format structure, allowing successful parsing of previously
failing bank statements.

erpnext/accounts/doctype/bank_statement_import/bank_statement_import.py

@@ -112,6 +112,32 @@ class BankStatementImport(DataImport):
 
 
 @frappe.whitelist()
+def preprocess_mt940_content(content):
+	"""Preprocess MT940 content to fix statement number format issues.
+
+	The MT940 standard expects statement numbers to be maximum 5 digits,
+	but some banks provide longer statement numbers that cause parsing errors.
+	This function truncates statement numbers longer than 5 digits to the last 5 digits.
+	"""
+	# Pattern to match :28C: field with statement number and optional sequence
+	pattern = r'(:28C:)(\d{6,})(/\d+)?'
+
+	def replace_statement_number(match):
+		prefix = match.group(1)  # ':28C:'
+		statement_num = match.group(2)  # The statement number
+		sequence_part = match.group(3) or ''  # The sequence part like '/1'
+
+		# If statement number is longer than 5 digits, truncate to last 5 digits
+		if len(statement_num) > 5:
+			statement_num = statement_num[-5:]
+
+		return prefix + statement_num + sequence_part
+
+	# Apply the replacement
+	processed_content = re.sub(pattern, replace_statement_number, content)
+	return processed_content
+
+
 def convert_mt940_to_csv(data_import, mt940_file_path):
 	doc = frappe.get_doc("Bank Statement Import", data_import)
 
@@ -124,7 +150,9 @@ def convert_mt940_to_csv(data_import, mt940_file_path):
 		frappe.throw(_("MT940 file detected. Please enable 'Import MT940 Format' to proceed."))
 
 	try:
-		transactions = mt940.parse(content)
+		# Preprocess MT940 content to fix statement number format issues
+		processed_content = preprocess_mt940_content(content)
+		transactions = mt940.parse(processed_content)
 	except Exception as e:
 		frappe.throw(_("Failed to parse MT940 format. Error: {0}").format(str(e)))