test(s7): live python-snap7 coverage for the #632/#638 codecs, TSAP override and PDU size (#632)

Extends the s7_1500 profile (DB1 2048 bytes, 'hex' seed type) with distinct
non-zero seeds for STRING/WSTRING/CHAR/WCHAR/DTL/DATE/TOD/TIME/S5TIME plus
undecodable buffers; S7_1500CodecTests covers reads, BadOutOfRange paths,
write round-trips (S7_SIM_ALLOW_WRITES=1), TSAP keys and negotiated PDU size.
Skips when S7_SIM_ENDPOINT is unreachable.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/drivers/S7.md

@@ -286,7 +286,10 @@ fresh drop after a healthy period reconnects immediately; worst-case recovery la
 - **Unit tests** — `tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.S7.Tests/` cover the
   address parser, the reinterpret/box conversions, and the driver lifecycle.
 - **Integration fixture** — a Docker S7 simulator on the shared docker host; see
-  [S7-Test-Fixture.md](S7-Test-Fixture.md) for the coverage map and endpoint.
+  [S7-Test-Fixture.md](S7-Test-Fixture.md) for the coverage map and endpoint. The wide/date-time
+  codecs (STRING, WSTRING, CHAR, WCHAR, DTL, DATE, TOD, TIME, S5TIME) and the TSAP override keys have
+  live snap7 coverage in `S7_1500CodecTests`; an unrepresentable STRING/DT write is `BadOutOfRange`
+  (not a comms fault) like the other codecs.
 - **CLI** — [Driver.S7.Cli.md](../Driver.S7.Cli.md) documents the standalone
   read/write/probe CLI for manual checks against a real or simulated CPU.