Remove redundant reassure tests and improve documentation

[mountiny]

Coming from this proposal in Slack.

Problem:

There are redundant/flaky performance tests in the Reassure suite. These tests are difficult to maintain and provide low value, as their scenarios are already covered elsewhere or offer little regression detection. This creates unnecessary complexity, slows down the test suite, and increases the likelihood of false positives.

Solution:

Remove the redundant tests that verify scenarios already covered in separate tests. Eliminate tests that check interactions with minimal impact on regression detection. Focus on retaining tests that provide high-value regression coverage, and reorganize the test suites for better maintainability by moving essential tests to lower levels where they are easier to manage.

• Move the reassure test documentation to the contributingGuidelines
• Update the guidelines to provide more guidance on how to prevent adding any redundant tests

[melvin-bot]

Triggered auto assignment to @strepanier03 (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.

[OlimpiaZurek]

Hi! I'm Olimpia from Callstack and I'd like to work on this issue.