feat: add validation to prevent transmitting edocuments with mismatched invoice IDs

[maasanto]

Problem

If an invoice is submitted after its edocument is created, the source document reference may be updated but the XML content still contains the old draft invoice ID. This could result in transmitting incorrect invoice data.

Solution

Added comprehensive validation to transmit_edocument() through a new _validate_edocument_for_transmission() function that verifies:

1. Edocument profile is configured
2. XML validation status is successful
3. Source document is submitted (docstatus == 1) for outgoing documents
4. Invoice ID in XML content matches the source document name for outgoing documents

If validation fails, transmission is blocked with a clear error message instructing the user to regenerate the edocument.

Technical Details

• Extracted existing validation checks into dedicated _validate_edocument_for_transmission() function
• Added XML parsing to extract invoice ID using XPath for both UBL (cbc:ID) and CII (rsm:ExchangedDocument/ram:ID) formats
• ValidationErrors are re-raised without wrapping to provide clean error messages to users
• Only validates source document status and XML ID for outgoing documents with source documents

Related

• Complements fix in edocument app (bug: draft name of sales invoice is used after submit edocument#21) by adding defensive validation at transmission time