Diff lines, opcodes, and chunks are now all explicitly typed, and we made a few tweaks for correctness (such as using `None` for the line numbers for the "other" side of an inserted/deleted chunk instead of an empty string). This change updates the unit tests that touch these types to make sure we're always fully defining the structures. Many of these tests used partial dictionaries for chunks, or even used dictionaries with integer keys instead of tuples for lines. This of course was flagged by the type checker. Testing Done: Ran unit tests.