Drop casts to a value's own type

`ziran check --lint` found three casts that convert a value to the type
it already has: two cast(float64) on float64 parts of a number and one
cast(u8) on a byte. They are removed. `make test` still passes with the
pinned Ziran.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>