Warnings from rust nightly

[oscargus]

It seems like some additional dead code analysis was introduced in the most recent nightly:

warning: field `0` is never read
  --> FastWaveBackend/src/vcd/reader.rs:12:24
   |
12 | pub(super) struct Line(pub(super) usize);
   |                   ---- ^^^^^^^^^^^^^^^^
   |                   |
   |                   field in this struct
   |
   = note: `Line` has derived impls for the traits `Clone` and `Debug`, but these are intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
12 | pub(super) struct Line(());
   |                        ~~
warning: field `0` is never read
  --> FastWaveBackend/src/vcd/utilities.rs:14:16
   |
14 |     OtherValue(char),
   |     ---------- ^^^^
   |     |
   |     field in this variant
   |
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
   |
14 |     OtherValue(()),
   |                ~~