[EPIC] Verify Pendulum DateTime parity with clj-oa3 (Option C); README

[dcj]

Summary

Part of the cross-repo ZonedDateTime end-to-end migration. python-oa3 is already compliant — uses pendulum.DateTime (zone-aware) end-to-end, parses any RFC 3339 offset including Z. This issue tracks verification + README documentation, not code changes.

Work

• Verify Pendulum behaviour against clj-oa3's new ZonedDateTime outputs (after clj-oa3 epic lands). Round-trip tests: parse a wire string, serialise, ensure exact equality.
• Add a "Time and timezones" section to README documenting:
  • Coercion: returns pendulum.DateTime (zone-aware)
  • Zone source: wire string offset; preserved. Z, +00:00, -07:00 all supported.
  • Round-trips cleanly via .to_iso8601_string()
  • Cross-implementation parity with clj-oa3 (after clj-oa3 epic)
• Note in README that this library is the reference compliant implementation of the standing zone-handling rule.

Cross-references

• Parent epic: https://github.com/grid-coordination/clj-price-server/issues/5
• Design: https://github.com/grid-coordination/clj-price-server/blob/main/doc/time-alternatives.md