rustfmt: Enable error_on_line_overflow

[divergentdave]

This enables error_on_line_overflow, which makes rustfmt throw an error on long lines it can't reformat, with exceptions for long strings and comments. I manually reformatted or rewrote code to fix the issues this found. This resulted in some other automatic formatting changes shaking out from running rustfmt again. The issues broke down as follows:

• Long lines in macro calls. These do not get reformatted because each macro makes its own DSL.
• A combination of long method names and turbofishes. In these cases I wrapped the turbofish across multiple lines. This transformation isn't typically performed by rustfmt AFAIK, but we do so frequently throughout the codebase.
• Long string literals. While a line with a long string literal itself doesn't result in an error being raised, it can prevent rustfmt from reformatting nearby code with long lines. I fixed these cases by extracting a variable or adding an escaped newline.
• Long patterns. I turned one long if-let into a match, thus moving the pattern onto a second line. I added some intermediate variables or renamed a variable in cases where a tuple destructuring got too long.