refactor: remove usage of NumberUtils

[BobDu]

ref: #41 (comment)

I created a test case and run the unit test on the pre-refactored and post-refactored versions, and both passed successfully.

Testing done

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[basil]

Thanks Bob. Ideally for changes that are slightly more risky like this, we'd do testing with the core test suite, PCT, and ATH. I'll run these tests after merging this and update the links here so you can see how I did it. If you (or someone else) ever does prepare a core PR to remove Commons Lang 2, we'd definitely want those tests run for that.

[basil]

@BobDu I tested this PR (and all your other changes) here:

• Fast incremental jenkins#8608
• Test JSON library changes acceptance-test-harness#2112
• Test JSON library changes bom#5425

Those 3 PRs show how to run a comprehensive set of tests on a given change.

I found only one small test-only regression in the Pipeline: Nodes and Processes plugin. I opened a PR to fix that here:

• Remove use of JsonSlurper workflow-durable-task-step-plugin#467