Add --metadata mode to InteropTest sample for metadata date/time and compression interop

[ritchiecarroll]

Summary

Adds a --metadata mode to the InteropTest-gsf sample so it can act as the C# subscriber side of a cross-language harness that verifies the STTP Python publisher's metadata interop — both XML xs:dateTime serialization and the GZip compression handshake — against the .NET DataSet parser.

Companion to sttp/pyapi#10 (the Python-side fixes + orchestrator).

What changed

src/samples/InteropTest-gsf/Program.cs (existing measurement-export behavior is unchanged when the flag is absent):

• New InteropTest HOSTNAME PORT --metadata [--gzip] mode. On connect it calls RefreshMetadata(), then:
  • on MetaDataReceived — writes metadata-received.xml, prints every DateTime column value, and exits 0;
  • on ProcessException (a malformed xs:dateTime, or an unexpectedly gzip-compressed payload, makes DataSet.ReadXml throw) — exits non-zero;
  • on a 15 s timeout — exits non-zero.
• --gzip advertises CompressionModes.GZip (compressed-metadata path). Without it, the .NET-default operational modes are used (CompressMetadata without GZip → uncompressed path) — the path a correctly-behaving publisher must serve uncompressed.

How it was verified

Driven by the harness in sttp/pyapi (test/interop/run_metadata_interop.py) against a live Python publisher, in both compression negotiations:

• fixed publisher → C# parses DeviceDetail.UpdatedOn = 2033-03-03T03:33:33.123 and exits 0 (uncompressed and GZip);
• reverted date fix → '2033-03-03T03:33:33.123+00:Z' is not a valid AllXsd value;
• reverted compression fix (plain negotiation) → hexadecimal value 0x1F, is an invalid character.

Reviewer notes

• Pairs with Fix metadata xs:dateTime serialization and GZip compression handshake for C# subscriber interop pyapi#10.
• The C# library was not modified. In some environments the from-source sttp.gsf.sln build fails because the bundled depends\GSF\GSF.Core.dll is out of sync with the source (a [Label] attribute-target mismatch); the harness compiles this sample against the prebuilt build\output\*\lib assemblies instead.

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