Add correctness, rule-consistency, and currency metrics

[jb3rndt]

This PR is based on #3, but I'm opening this already to get your feedback :)

Adds three new metrics:

• correctness: compares each data point with its ground truth using a distance function (either simple absolute difference for numbers or levenshtein distance for strings)
• currency: given a decline rate per column, the name of the column that contains the assessment date of each value in the tuple, and optionally a simulated assessment date to not rely on "now", calculates the currency based on this formula: curr(w, A) = exp(-decline(A) * age(w,A)) (with w the attribute value and A the column)
  • the decline rate is interpreted in years right now. It might be useful to make that configurable too?
• rule-based consistency: checks whether the given rules per column hold on an attribute. Weighing a rule happens inside the rule definition itself. The return value of all rules are just added up when assessing the consistency value.
  • since rules are defined as python functions right now, I allowed metrics to be initialized by passing a config object directly (keeping JSON as an option too of course)

[Copilot]

Pull Request Overview

This PR introduces three new data quality metrics (Correctness, Currency, and Rule-based Consistency), refactors writer implementations to use a shared SQLAlchemy-based DatabaseWriter, and adds a SQLAlchemy ORM model for persisting results.

• New metrics: Correctness (distance vs. ground truth), Currency (exponential decay by age), Rule-based Consistency (rule aggregation with certainty).
• Refactor: Unify SQLite/Postgres writers via DatabaseWriter and SQLAlchemy ORM models; add DQDimension enum and update DQResult to use it.
• Config handling: Add MetricConfig base and load_config utility; allow passing config objects (notably for rule-based consistency).

Reviewed Changes

Copilot reviewed 18 out of 21 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
metis/writer/sqlite_writer.py	Switch SQLiteWriter to SQLAlchemy via DatabaseWriter; provide engine factory.
metis/writer/postgres_writer.py	Switch PostgresWriter to SQLAlchemy via DatabaseWriter; provide engine factory.
metis/writer/database_writer.py	New base writer using SQLAlchemy ORM models; centralizes table creation and writes.
metis/writer/console_writer.py	Minor typing tweak for optional config.
metis/utils/result.py	DQdimension type changed to DQDimension enum.
metis/utils/dq_dimension.py	New DQDimension StrEnum with dimensions.
metis/models.py	New SQLAlchemy declarative model and dynamic table registration.
metis/metric/metric.py	Add MetricConfig support and config loader.
metis/metric/currency/currency.py	Implement Currency metric with exponential decay by age.
metis/metric/currency/config.py	Config dataclass for Currency.
metis/metric/correctness/correctness.py	Implement Correctness metric (distance-based).
metis/metric/consistency/rule_consistency.py	Implement rule-based consistency with certainty annotation.
metis/metric/consistency/consistency.py	Make Consistency accept JSON config path; switch to DQDimension.
metis/metric/consistency/config.py	Config dataclasses for consistency metrics.
metis/metric/config.py	Base config dataclass helper.
metis/metric/completeness/completeness.py	Switch to DQDimension and updated typing.
metis/metric/init.py	Export new metrics.
metis/dq_orchestrator.py	Allow MetricConfig object in orchestrator assess API.

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