Overview
This PR introduces an initial (beta) build path for OMOP Waveform Extension ETL tables using pre-extracted waveform metadata inputs.

Context
The Python waveform metadata extraction process is currently maintained in a separate repository. Once that process is finalized, it may be incorporated into this repository.

Source metadata inputs
The ETL expects two source tables populated by the extraction script:

waveform_files_all
subject_id, person_id, hadm_id, visit_occurrence_id, visit_detail_id, location, waveform_folders, record_id, group_id, mimic_start, mimic_end, session_start, session_end, file_start, file_end, src_file, trg_file

waveform_channels_all
person_id, visit_occurrence_id, visit_detail_id, group_id, session_start, session_end, file_start, file_end, src_file, trg_file, channel_name, sample_units, sample_rate, sample_rate_units, gain, gain_units, segment_length

What this PR includes:

• Adds initial SQL ETL build logic for OMOP Waveform Extension targets.
• Uses waveform_files_all and waveform_channels_all as source metadata interfaces.
• Applies waveform-specific concept mappings as part of the build. Some waveform-specific vocabulary content is currently supplied via the Tufts CVB repository, and additional terms/mappings will be added over time.

Scope and maturity
This PR establishes the initial/beta end-to-end waveform ETL framework and will be expanded and refined in subsequent updates.

Out of scope
This PR does not build the WAVEFORM_FEATURE table.