fix: handlebars math helper handles large negative integers

[RafeArnold]

Currently, when the result of the handlebars math helper is a negative number less than java.lang.Integer.MIN_VALUE, it's incorrectly coerced into a java.lang.Integer. This PR fixes that.

References

Submitter checklist

• Recommended: Join WireMock Slack to get any help in #help-contributing or a project-specific channel like #wiremock-java
• The PR request is well described and justified, including the body and the references
• The PR title represents the desired changelog entry
• The repository's code style is followed (see the contributing guide)
• Test coverage that demonstrates that the change works as expected
• For new features, there's necessary documentation in this pull request or in a subsequent PR to wiremock.org

[dieppa]

LGTM