Add multi record test for `GetArithmeticTwap`, Add tests for `GetArithmeticTwapToNow`

[mattverse]

What is the purpose of the change

This PR adds multi-record test for GetArithmeticTwap in api_test.go in the existing test for GetArithmeticTwap. This PR also adds test cases for GetArithmeticTwapToNow using the existing test case for GetArithmeticTwap

Also added minor side comments on things I had to take time to find context on.

Brief Changelog

• Adds multi-record test for GetArithmeticTwap
• Adds test cases for GetArithmeticTwapToNow

Documentation and Release Note

• Does this pull request introduce a new feature or user-facing behavior changes? no
• Is a relevant changelog entry added to the Unreleased section in CHANGELOG.md? no
• How is the feature or change documented? not documented