Superfluous timeZone property for EnergyPlanTariffPeriod schema

[mattyp]

Description
At risk of dragging up scars from #613... the EnergyPlanTariffPeriod schema currently seems to have a timeZone property that doesn't add any value beyond what's already provided by ISO 8601 time formats and the parent electricityContract's timeZone property. Time zones can now be handled either through UTC offsets in the time strings themselves (like "15:00:00+10:00") or by falling back to the electricityContract's timeZone setting. Having an extra timeZone property at the tariff period level just adds confusion and complexity.

Intention and Value of Change
By removing this redundant property, we can:

• Make the schema cleaner and easier to understand
• Prevent confusion about which timeZone property takes precedence
• Make it clearer how time zones should be handled with relation to TOU rate boundaries

Area Affected
We need to update the EnergyPlanTariffPeriodV2 schema in the Energy APIs. Specifically:

• Remove the timeZone property from EnergyPlanTariffPeriodV2

Change Proposed

• Remove the timeZone property from EnergyPlanTariffPeriodV2

This change will simplify things while maintaining all the functionality we need for proper time zone handling in energy plans.

[mattyp]

Unless I've missed something, this redundant timeZone property should have been removed when the types for TOU rate boundaries were changed to ISO8601 (#613). If that's the case, this is potentially a minor change that could be considered for MI22 on #683???

[mattyp]

Descriptions for TOU rate boundaries already reference the electricityContract's timeZone property, rather than the tariffPeriod's timeZone property.

If the time is provided without a UTC offset, the time zone will be determined by the value of EnergyPlanContract.timeZone.

So there's no documentation that needs updating AFAIK.