feat: Add total slowest test + percent change resolvers in API

[ajay-sentry]

Purpose/Motivation

This PR aims to add resolvers for total_slowest_tests and similar percent change so we can link them up to the failed tests table

Also added related UT

Notes to Reviewer

Anything to note to the team? Any tips on how to review, or where to start?

Legal Boilerplate

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[codecov-notifications[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:white_check_mark: All tests successful. No failed tests found.

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.31%. Comparing base (3c2b4ff) to head (c39e06c). Report is 2 commits behind head on main.

:white_check_mark: All tests successful. No failed tests found.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #896 +/- ## ======================================= Coverage 96.31% 96.31% ======================================= Files 823 823 Lines 19084 19092 +8 ======================================= + Hits 18381 18389 +8 Misses 703 703 ``` | [Flag](https://app.codecov.io/gh/codecov/codecov-api/pull/896/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codecov) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/codecov/codecov-api/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codecov) | `92.66% <100.00%> (+<0.01%)` | :arrow_up: | | [unit-latest-uploader](https://app.codecov.io/gh/codecov/codecov-api/pull/896/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codecov) | `92.66% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=codecov#carryforward-flags-in-the-pull-request-comment) to find out more.

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