refactor(ecg): move flatline detection to EcgFeatures
- Add per-lead
m_FlatSampleCountstate initialized during extraction setup. - Add
IsLatestSegmentFlat()with a 200 ms consecutive-sample threshold. - Perform flatline detection in
ProcessSingleLead()before QRS processing. - Remove the global
HasFlatSegment()check fromEcgAnnotation. - Remove flatline checks from
GetQRS()andGetPTU(). - Remove the
pData.size() == m_LeadCountrestriction fromExctrationProcess(). - Add unit-test filter configuration for
EcgFeaturesTest.