Fix: Support BER long-form length encoding in AARE parsing

[marco92]

In the Application Association Response (AARE, aare.py), only ASN.1 BER short-form length encoding was previously supported. This caused parsing to fail for responses using long-form length encoding.

This change adds automatic detection of BER short-form vs long-form length encoding and correctly parses the length in both cases.

Reference (ASN.1 BER length encoding):
https://www.oss.com/asn1/resources/asn1-made-simple/asn1-quick-reference/basic-encoding-rules.html

This improves compatibility with DLMS/COSEM devices that encode AARE APDUs using BER long-form lengths.

Issue observed on "Kamstrup OMNIA® e-meter" and fix tested successfully.

[Krolken]

Nice catch. Are you using Public keys?

We have a simillar function for x-adr:

dlms-cosem/dlms_cosem/a_xdr.py

Line 50 in c52e9d4

def get_axdr_length(data: bytearray):

It would be nice if you could open an issue and provide some sample PDUs so I can write tests for it. I should also implement the same handling on all ASCE-services.

[marco92]

@Krolken I'm using HLS GMAC with symmetric keys. I created the following issue and also added HDLC PDUs:
#116