Fix source-backed Legacy SAS RCB export identity

[masarray]

Purpose

Match IEDScout semantics for source-backed RCB export without changing existing live-model exact-runtime export behavior.

A source SCL can describe one logical ReportControl name="Buffer" with RptEnabled max="2", while the online MMS runtime exposes concrete instances such as Buffer01 and Buffer02. When ARSAS selects one of those runtime slots from a source-backed row, the exported CID/IID must retain the logical source identity and indexing metadata, like IEDScout does, rather than serializing Buffer02 as a separate non-indexed SCL ReportControl.

Change

• add opt-in PreserveSourceReportControlIdentity to LegacySasSclExportOptions;
• when enabled, retain the source ReportControl name/indexing/RptEnabled metadata;
• default remains unchanged: exact runtime export still collapses to one non-indexed concrete instance and strips RptEnabled to prevent double suffixing;
• add regression coverage for both paths.

No MMS acquisition, report activation, control, runtime discovery, or trusted-SCL reporting behavior is changed.

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