Add configurable single booking support for SEPA Direct Debits (Sammellastschrift)

[timrasche]

This adds the ability to request individual bookings (einzelbuchungGewuenscht) for batch SEPA Direct Debits, matching the existing functionality already available in SendSEPATransfer.

Previously, einzelbuchungGewuenscht was hardcoded to false in SendSEPADirectDebit, meaning batch direct debits always appeared as a single aggregated entry on the bank statement — regardless of the caller's intent.

Changes:

• Added $singleBookingRequested property to SendSEPADirectDebit
• Added setSingleBookingRequested(bool): self setter method (consistent with SendSEPATransfer API)
• einzelbuchungGewuenscht now uses the configurable value instead of hardcoded false
• Updated __serialize() / __unserialize() to include the new property

Usage:

$action = SendSEPADirectDebit::create($account, $painXml);
$action->setSingleBookingRequested(true);

The bank-side parameter einzelbuchungErlaubt is still respected — the flag is only sent when the bank advertises support for it.

[Philipp91]

Now that PHP8 supports named arguments, have you considered using a create() parameter rather than adding a new setter? I believe this would be the only case in this library so far where a setter is used on an action.

[timrasche]

Yes, I initially considered that as well, but then decided against it because I adopted the approach from SEPATransfer, as I didn't want to have two different logics for the two similar cases. I just adapted it from SEPATransfer. Therefore, we should either switch both cases to named arguments, or leave it as it is.

[Philipp91]

Ah you're right, I overlooked that we have a setter there already, and even for exactly the same kind of property.

[nemiah]

Great! Merging…