feat(iso): add PosCapability for DE-027 encoding

[ar-agt]

Introduces PosCapability in org.jpos.iso for structured encode/decode of DE-027 (POS Capability).

Relationship to DE-022

DE-022 (PosDataCode) records what actually happened. DE-027 (PosCapability) records what the terminal is capable of. Sub-fields 27-1 and 27-2 share the same bit tables — so PosDataCode.ReadingMethod and PosDataCode.VerificationMethod are reused directly.

Wire layout (27 bytes fixed)

Sub-field	Name	Format
27-1	Card reading capability	B4 (bit-flags, same as DE-022 sf-1)
27-2	Cardholder verification capability	B4 (bit-flags, same as DE-022 sf-2)
27-3	Approval code length	N1 ASCII
27-4	Cardholder receipt data length	N3 ASCII
27-5	Card acceptor receipt data length	N3 ASCII
27-6	Cardholder display data length	N3 ASCII
27-7	Card acceptor display data length	N3 ASCII
27-8	ICC scripts data length	N3 ASCII
27-9	Track 3 rewrite capability	A1 Y/N
27-10	Card capture capability	A1 Y/N
27-11	PIN input length capability	B1 binary

Usage

PosCapability cap = PosCapability.builder()
    .readingCapability(PosDataCode.ReadingMethod.ICC)
    .readingCapability(PosDataCode.ReadingMethod.MAGNETIC_STRIPE)
    .verificationCapability(PosDataCode.VerificationMethod.ONLINE_PIN)
    .approvalCodeLength(6)
    .cardholderReceiptLength(40)
    .pinInputLength(12)
    .build();

msg.set(new ISOBinaryField(27, cap.pack()));

PosCapability received = PosCapability.unpack(msg.getBytes(27));
received.canReadICC();          // true
received.canVerifyOnlinePin();  // true
received.getPinInputLength();   // 12

Tests

35 tests — all passing.