Expose internal/external metadata flags in Config to prevent empty external metadata

[ritchiecarroll]

When a Python subscriber connects to the C# STTP publisher, metadata for external measurements can be silently excluded. Python defines OperationalModes.RECEIVEINTERNALMETADATA and RECEIVEEXTERNALMETADATA, but DataSubscriber._send_operationalmodes() sends neither flag, and neither Config nor Settings exposes an option to enable them.

The C# publisher's AcquireMetadata() interprets this combination by applying Internal <> 0 to MeasurementDetail and, unless MutualSubscription is enabled, OriginalSource IS NULL to DeviceDetail. Consequently, an external-only input selection produces an empty measurement metadata table even when the publisher's SQL returns the intended records.

Reproduction and confirmed workaround

1. Connect a Python Subscriber with the default Config to a C# STTP publisher whose selected measurements are external (Internal=0).
2. Request metadata, as the subscriber does automatically by default.
3. Observe that the returned MeasurementDetail table is empty.
4. Add the following flags in _send_operationalmodes() before sending DEFINEOPERATIONALMODES, then reconnect:

operationalModes |= OperationalModes.RECEIVEINTERNALMETADATA
operationalModes |= OperationalModes.RECEIVEEXTERNALMETADATA

Enabling these flags was confirmed to resolve the issue in the affected runtime. Offline examination of the corresponding database also showed that the publisher SQL selected 19 external measurements, 1 device, and 6 phasors; the existing metadata inclusion filters explain why those records were excluded. A version row can remain, so a successful response or positive aggregate metadata count does not establish that measurement metadata was received.

Requested change

Expose internal/external metadata inclusion as supported Python connection configuration, equivalent to the C# subscriber options:

config = Config(
    receiveinternalmetadata=True,
    receiveexternalmetadata=True,
)
subscriber.connect("publisher:port", config)

Suggested implementation:

• Add documented options and defaults to Config/Defaults.
• Propagate them to DataSubscriber in Subscriber._connect().
• Set the corresponding OperationalModes bits in _send_operationalmodes(), including on reconnect.
• Document the chosen defaults and their compatibility implications. Explicit configuration should allow external metadata regardless of the default policy.
• Add tests for flag combinations and configuration propagation, ensuring compression/version/encoding bits are preserved.

Relevant source

• Python operational-mode construction — _send_operationalmodes()
• Python connection configuration
• Python configuration propagation — _connect()
• C# publisher — AcquireMetadata()

Config.metadatafilters cannot provide this behavior: those expressions further restrict metadata and do not override the internal/external inclusion flags. Currently, an application must modify the library or intercept the outgoing operational-mode command to request both categories.