Clarify FAT timestamp hover as decoded precision evidence

[masarray]

Supersedes #166 on latest main

main advanced with #165 while #166 was validating. To avoid merging a stale branch and losing forward progress, this PR reapplies the exact already-validated two-file wording/test blobs directly on top of current main d5a08bb4....

Evidence wording correction

ARSAS now preserves the full decoded IEC 61850 timestamp through the fixed ARIEC61850 engine. It does not yet retain the exact original 8-byte UTC-Time wire payload in FAT evidence.

This changes the tooltip label from Raw IED timestamp (full precision) to Decoded IED timestamp (full precision) so customer-facing evidence does not overstate provenance.

Scope

• exactly one production string changed in IoTestModels.cs;
• focused tooltip regression requires the new wording and rejects the old raw-wire claim;
• no timestamp value, rounding, FAT workflow, evidence storage, polling/report behavior, MMXU Fix live MMXU power measurements #165 behavior, or UI layout changes.

Merge only after CI on this exact latest-main integration head is green and main is rechecked immediately before merge.