[P1][Sprint 1][Parity] Add typed Spreads and market Indicators resources

[karlwaldman]

Why

The published API contract includes /v1/spreads/* and /v1/indicators/* operations. Node has typed resources; Python has neither. oilpriceapi.analysis is local calculation and is not API endpoint coverage.

Acceptance criteria

• Implement typed sync and async methods for the published spreads and indicators operations selected by the support manifest.
• Preserve timestamps, provenance, units, nulls, and pagination.
• Cover valid envelopes, malformed 200 responses, 401/402/403/429, no-data, and timeout recovery.
• Add examples, reference docs, and live smoke coverage.
• Update machine-readable capabilities and cut a minor release.

Delivery

Python package release; independent of Rails/web.