Replace environments.yml with environments.py

[OmerBaddour]

Summary

• ~/.clair/environments.yml is replaced by ~/.clair/environments.py, loaded via importlib
• Environment.routing now accepts any Callable[[str, str, str], str] alongside the existing RoutingConfig subclasses — callable receives (database, schema, table) as separate args
• InvalidRoutingPolicyError removed; InvalidEnvironmentsFileError added for malformed .py files
• write_environments_yml → write_environments_py; scaffold template updated to Python

Example config:

from clair.environments import Environment

environments = {
    "dev": Environment(
        account="myorg-myaccount",
        user="me@example.com",
        warehouse="my_wh",
        routing=lambda db, schema, table: f"{db}_dev.{schema}.{table}",
    ),
}

Test plan

• uv run pytest tests/ — 494 passed

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