refactor: improve and test parseIntWithDefault utility

[dudantas]

Moved parseIntWithDefault to its own module for reuse and improved handling of null, undefined, and NaN values.
Added comprehensive tests for parseIntWithDefault and configured a separate tsconfig for running tests.
Updated package.json with a test script.

[Copilot]

Pull Request Overview

This PR refactors the parseIntWithDefault utility function by extracting it into a separate module for reusability and improving its handling of edge cases like null, undefined, and NaN values. It also adds comprehensive test coverage and configures a test environment.

• Extracted parseIntWithDefault from the server file into a standalone module
• Enhanced the function to properly handle null, undefined, and NaN values
• Added comprehensive test suite with 10 test cases covering various input scenarios

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tsconfig.tests.json	New TypeScript configuration for running tests
tests/parseIntWithDefault.test.ts	Comprehensive test suite for the parseIntWithDefault utility
src/routes/api/outfits/parseIntWithDefault.ts	New module containing the improved parseIntWithDefault function
src/routes/api/outfits/+server.ts	Updated to import parseIntWithDefault from the new module
package.json	Added test script to run the parseIntWithDefault tests

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