Release 1.9.0: Develop to main

[ygit]

Description

Version 1.9.0

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Pre-launch Checklist

• [x] The Documentation is updated accordingly, or this PR doesn't require it.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] I listed at least one issue that this PR fixes in the description above.
• [x] I added new tests to check the change I am making, or this PR is test-exempt.
• [x] All existing and new tests are passing.