Support requesting specific resolution

[slovdahl]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for requesting specific price resolution intervals when fetching energy prices. The main change allows users to specify a 15-minute resolution interval in addition to the default 60-minute resolution.

• Added a resolution parameter to the energy_prices method with support for 15 and 60-minute intervals
• Added validation to reject unsupported resolution values
• Added comprehensive test coverage for the new 15-minute resolution functionality

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tests/test_models.py	Added tests for 15-minute resolution and unsupported resolution validation
tests/fixtures/energy-15-min.json	Added fixture data for 15-minute resolution testing
spothinta_api/spothinta.py	Modified energy_prices method to accept resolution parameter with validation

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