Add TimescaleDB meter reading aggregation design handover documentation

[eshandilcsumb]

Description

This pull request adds a design handover document for the TimescaleDB meter reading aggregation implementation.

The purpose of this document is to provide maintainers and future contributors with a complete overview of the new reading aggregation architecture, including data flow, database objects, refresh and rebuild behavior, conversion lifecycle, query integration, operational considerations, known limitations, and remaining work.

The document describes the implementation currently available on the timeVary2026Summer branch, including:

• Raw reading ingestion and batching behavior.
• The hour- and conversion-aware split hypertable design.
• Meter and group continuous aggregates.
• Group dependency caches and revision tracking.
• Refresh and rebuild orchestration.
• Time-varying conversion integration.
• Query and indexing optimizations.
• Current deployment limitations and migration requirements.
• Future performance and operational tuning opportunities.

The motivation for this document is to preserve architectural context and implementation decisions as the TimescaleDB migration progresses. It is intended to help reviewers, maintainers, and future contributors understand both the current design and the remaining work needed before production deployment.

Some links in this document reference source files introduced by the associated TimescaleDB implementation pull request. These links will resolve once that pull request #1690 is merged into the repository.

Contributors:

• @eshandilcsumb
• @MartinCSUMB

Type of change

• Note merging this changes the database configuration.
• This change requires a documentation update

Checklist

• I have followed the OED pull request ideas
• I have removed text in ( ) from the issue request
• I acknowledge that every person contributing to this work has signed the OED Contributing License Agreement and each author is listed in the Description section.

Limitations

• This document describes the current implementation state and does not itself introduce database or application changes.
• Some source file references may need future updates if repository structure changes.
• The document reflects the current TimescaleDB implementation state and may need updates as migration support, production benchmarking, and operational tuning are completed.

[huss]

@eshandilcsumb & @MartinCSUMB Thank you for this contribution. Please see the other PR from your team about the needed CLA.