Problem

• test file was in src folder hence, included in the distribution,
  which increases unnecessary increase in bundle size,
• tests were all in one file, risking E2BIG errors as the file size grew
• difficult to manage and locate specific tests
• running tests in a single file can be inefficient and error-prone

Solution

• moved tests to separate files in the tests folder to prevent file size issues
• seperated test file into multiple test files for better organisation
• added esbuild register to test esm code (default npm run test behavior)
• added steps to test cjs build with tsc (in ci esm and cjs both should be tested)
• removed tsup from package dev dependencies

this change improves test organization, stability, and enhances testing capabilities without increasing the binary size.