Add test for hasDayWithoutBirds method

[rabestro]

pull request

• Added a test to validate the behavior of hasDayWithoutBirds when the last day has zero visits.
• Updated the lastWeek field to be final and align with best practices.

https://forum.exercism.org/t/bird-watcher-in-java-should-we-add-a-test-case/17933

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This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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[no important files changed]

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[jagdish-15]

@kahgoh The forum topic doesn’t appear to have a clear resolution. What do you think, should this be merged with the [no important files changed] label, or not?

@rabestro Would love to hear your thoughts on this as well.

[kahgoh]

As suggested on the forums, I think we can add this test and disable re-running of the tests.