fix: Ensure all headers in the same package have the same copyright year

[danieljbruce]

Description

Solves issue googleapis/librarian#4753. Ensures that all headers in files of the same package have the same copyright year. Files containing no copyright year also now have a copyright year as this was a related issue discovered by the testing script.

Impact

Assists with librarian migration from https://github.com/googleapis/librarian/milestone/88.

Testing

The root directory of google-cloud-node doesn't use CI tests, but I created a check-package-years.sh script in the bin folder that only succeeds if all header files have the same copyright year for every file in a given package.

Additional information

Headers with copyright years needed to be generated for some files:

Some .jsdoc generation files will also generate headers for 2026 which is desirable:

[pearigee]

Can we skip the proto files? They are just copied artifacts from google3 and the changes may not stick.

[pearigee]

Also, it looks like the snapshot testing in the unit tests may have broken as a result of this?

[danieljbruce]

Also, it looks like the snapshot testing in the unit tests may have broken as a result of this?

Ah. Ok. This is a good catch. I thought the presubmit / units test weren't required, but the snapshots definitely should match.

[danieljbruce]

Also, it looks like the snapshot testing in the unit tests may have broken as a result of this?

Ah. Ok. This is a good catch. I thought the presubmit / units test weren't required, but the snapshots definitely should match.

Also, it looks like the snapshot testing in the unit tests may have broken as a result of this?

Ah. Ok. This is a good catch. I thought the presubmit / units test weren't required, but the snapshots definitely should match.

The snapshot testing has been addressed, but the log for the other tests gets truncated.