Add EX530v v1.0 key, encode branch, and raise config size limit

[guness]

Adds support for the TP-Link EX530v v1.0, an ISP-customized VDSL gateway (seen on Turkcell Superonline in Turkey). None of the six existing keys decrypt its conf.bin.

Tested against a real backup from an EX530v v1.0, firmware EX530v-v1.0_250415_2424.

Changes

1. New key ex530v-v1 = 40 BA C6 6C CA 5A 1C FE

Recovered by brute force rather than firmware extraction — TP-Link does not publish firmware for this ISP-locked model. The search was made tractable by the structure the existing ISP keys already share (byte6 == 0x1D, byte7 ∈ {FE,FD}, byte0 ∈ 0x40..0x47) plus the fact that DES ignores each key byte's LSB as a parity bit, which cuts the space 32×.

It is confirmed by the config's own MD5 self-check, and the decrypted XML contains <X_TP_DeviceModel val=EX530v(EU)/>. Note this is the parity-normalized form; TP-Link's original is presumably 40 BB C7 6D CA 5B 1D FE, which DES treats identically.

2. Encode branch for EX530v

Without it, xml -> bin silently falls through to the default key and produces a file the router will reject. Mirrors the existing XZ005-G6 branch, including forcing little-endian.

3. MAX_SIZE = 0x40000, replacing three hardcoded 0x20000 limits

This is the one change that affects other models, so flagging it explicitly. The EX530v's uncompressed XML is 138160 bytes (~135 KiB), over the old 0x20000 ceiling, so decoding failed twice: first in the input-size guard when re-encoding, then in check_size_endianness with "compressed size too large for a TP-Link config file!".

The limit also serves as the endianness heuristic, so raising it does weaken that slightly — it now only auto-flips when a byteswapped size exceeds 256 KiB rather than 128 KiB. In practice a wrong-endian read is off by orders of magnitude (this file reads as 2954560000 big-endian vs 138160 little-endian), so detection still works. Happy to bump it to a smaller value, or gate it per-model, if you'd prefer something more conservative.

Verification

$ ./tpconf_bin_xml.py -l conf.bin conf.xml
OK: appears your device uses little-endian.
OK: BIN file decrypted, MD5 hash verified, uncompressing…
Done.

Round-trip conf.bin -> conf.xml -> conf.bin' -> conf.xml' produces byte-identical XML. The re-encoded .bin is smaller than the original (21152 vs 21904 bytes) because this compressor packs tighter than the router's, which is expected and also true of the already-supported models.

Caveat: I have not restored a re-encoded file to the device, so the encode path is verified only by round-trip, not by the router accepting it.

Note for EX530v users

The device is little-endian, so decoding needs -l. README updated accordingly.