Add detailed EIA-176 continuation-line tables

[MeadBarrel]

Overview

Closes #5240.

What problem does this address?

EIA-176 continuation-line data includes useful detail behind several aggregate gas supply and disposition fields, but these records were only available in raw_eia176__continuation_text_lines. This PR exposes the detailed records for imports, supplemental gaseous fuels, exports, and other disposition as core tables while preserving the existing aggregate disposition table.

What did you change?

• Added four EIA-176 core tables from continuation-line records:
  core_eia176__yearly_gas_imports, core_eia176__yearly_supplemental_gaseous_fuel_supplies,
  core_eia176__yearly_gas_exports, and core_eia176__yearly_gas_disposition_other.
• Normalized continuation-line state/reference codes, fuel types, transportation modes, destination classifications, and lightly normalized free-text Line 18.4 disposition types.
• Aggregated duplicate continuation-line records into stable table rows and added bounded total checks against the corresponding reported company-level values.
• Added resource/field metadata, EIA-176 fuel-type enums, Alembic migrations, dbt source schemas, and row-count expectations for the new tables.
• Updated core_eia176__yearly_gas_disposition metadata to point users to the new detailed exports and other-disposition tables.

Documentation

Make sure to update relevant aspects of the documentation:

• Update the release notes: reference the PR and related issues.
• Update relevant Data Source jinja templates (see docs/data_sources/templates).
• Update relevant table or source description metadata (see src/metadata).
• Review and update any other aspects of the documentation that might be affected by this PR.

Testing

Suggested reviewer checks:

pixi run --frozen pytest --no-cov test/unit/metadata_test.py::test_field_definitions test/unit/metadata_test.py::test_resource_descriptors_valid
pixi run --frozen dg check defs --verbose
pixi run dbt_helper validate --asset-select "key:core_eia176__yearly_gas_imports or key:core_eia176__yearly_supplemental_gaseous_fuel_supplies or key:core_eia176__yearly_gas_exports or key:core_eia176__yearly_gas_disposition_other"

To-do list

• If updating analyses or data processing functions: make sure to update row count expectations in dbt tests.
• Run pixi run prek-run to run linters and static code analysis checks.
• Run pixi run pytest-ci locally to ensure that the merge queue will accept your PR.
• Review the PR yourself and call out any questions or issues you have.
• For PRs that change the PUDL outputs significantly, run the full ETL locally and then run the data validations using dbt. If you can't run the ETL locally then run the build-deploy-pudl GitHub Action manually and ensure that it succeeds.

[e-belfer]

You're making great headway! Some requests for field changes and document updates, and a few questions.

[MeadBarrel]

Ok, so i currently have reference_state renamed to supplier_location_code alongside supplier_location_type (subnational/national_or_other) for line 300, mimicking line 1400's destination_code and destination_type. Company name columns are named supplier_name and recipient_name.

I'm thinking, however, maybe it would be better to unify those, like counterparty_location_code, counterparty_location_type and counterparty_name?

[e-belfer]

@MeadBarrel thanks for all of your work on this one! I think it's ready to go, but because it's such a big pr I've tagged @cmgosnell for secondary review.

@cmgosnell Tagging you for secondary review, after alembic update and resolution of merge conflicts.