Move formatting preservation tests to rule-specific test files

[Copilot]

The formatting-preservation-test.rkt file contained tests verifying that refactoring rules preserve formatting of unmodified code. These tests were separated from the other tests for the same rules, making them harder to maintain.

Changes

• Moved nested or formatting test → boolean-shortcuts-test.rkt
• Moved let-to-define and define-let-to-double-define formatting tests → let-replacement-test.rkt
• Moved cond-let-to-cond-define formatting test → cond-let-replacement-test.rkt
• Deleted formatting-preservation-test.rkt

Each test now lives alongside other tests for its corresponding rule, making the test suite structure more consistent with the rest of the codebase.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Formatting preservation test cases should be split up</issue_title>
<issue_description>The formatting-preservation-test.rkt file contains a handful of test cases that check that various Resyntax rules don't reformat more code than expected. But those sorts of tests are also spread across the rest of Resyntax's test suite, alongside other tests for the rule in question. Since this behavior is (mostly) up to the rule to handle correctly, it would make more sense for the tests in formatting-preservation-test.rkt to be moved to the existing rule-specific test files.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Formatting preservation test cases should be split up #644

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