Enable warnings for clippy::cast_possible_truncation

This commit enables Clippy lint checks for truncating conversions. All
code changes to conform to this are included in earlier commits.

Signed-off-by: Jonathan Browne <12983479+JBYoshi@users.noreply.github.com>

.cargo/config

@@ -4,6 +4,7 @@ rustflags = [
   "-Wclippy::ptr_as_ptr",
   "-Wclippy::undocumented_unsafe_blocks",
   "-Wclippy::cast_lossless",
+  "-Wclippy::cast_possible_truncation",
   "-Wclippy::cast_possible_wrap",
   "-Wclippy::cast_sign_loss",
   "-Wmissing_debug_implementations",