v3.25.7: the ENVELOPE response-bytes fetch

The live report: an SPI2 01 secured packet reported no PoR.  For such a
packet TS 31.115 4.2/4.4 (b6=0) has the Response Packet retrieved by the
ME from the ENVELOPE exchange (SEND SHORT MESSAGE is the b6=1 case), but
_send_envelope only asked for response bytes after a 61xx answer - the
card signals them with 62xx/63xx instead (the "more data" quirk the
remote-command SWs already acknowledge, _ram_remote_sw_ok), so the whole
PoR stayed on the card and the late-PoR STATUS poll found nothing.

_envelope_get_response (shared with _send_event_download, which had the
same 61xx-only code): a 61xx names the GET RESPONSE length; a 62xx/63xx
without data gets Le 256 (00c0000000 - a bare 61 no longer emits the
odd-length '%02x' % 0x100 APDU).  The result is adopted when bytes were
delivered (or for a 61xx); otherwise the warning stays, so the v3.6.58
SEND-SM PoR path (the STATUS poll) keeps working.

Tests: the 61xx length, the 63xx+PoR fetch (Le 256), the bare-61
encoding, the warning-kept path (the poll still runs) and the
event-download sharing.  887 frontend + 880 Python; sw cache simple-v431.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pysim-simple-server"
-version = "3.25.6"
+version = "3.25.7"
 description = "HTTP REST server wrapping pysim for the SIMple PWA"
 requires-python = ">=3.8"
 # pysim is a git-only dependency installed explicitly by setup.bat/setup.sh.